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Double skin façade in hot arid climates: computer simulations to find optimized energy and thermal performance of double skin façades

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Double skin façade in hot arid climates: computer simulations to find optimized energy and thermal performance of double skin façades

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Content 1

DOUBLE-SKIN FAÇADE IN HOT-ARID CLIMATES
COMPUTER SIMULATIONS TO FIND OPTIMIZED ENERGY AND THERMAL
PERFORMANCE OF DOUBLE SKIN FACADES

by

Zakarya A. Alahmed

A Thesis Presented to the
FACULTY OF THE USC SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF BUILDING SCIENCE

AUGUST 2013

Copyright 2013 Zakarya A. Alahmed
1

Acknowledgements

I would like to express my deepest gratitude to my thesis committee for their guidance
and support. Prof. Douglas Noble my thesis chair who is not only gave me guidance and
support in my thesis, but he helped me and supported me while I had a life crises, prof.
Marc Schiler, who was giving guidance and encouragement from his extensive
knowledge and experience with kindness and encouragement, prof. Joon-Ho Choi, who
enriched this work with technical and detailed topics, in addition to his friendly
personality, Jeffery Vaglio, who helped to me erect the base of this work, based on his
wide experience in double skin facades technologies. I am also thankful for the assistance
and support given by Peter Simmond, Jeffery Landreth and Ilaria Mazzoleni.
I am grateful and thankful to the most precious thing I have in my life, my parents, my
brothers, Lama, my lovely wife for her support and encouragement, and my adorable
child Maria who was born at the beginning of my enrolment in the MBS program.
Special thanks to all my colleagues in the MBS program, who shared with me their
helpful thoughts and comments.

2

Table of contents
Acknowledgements ............................................................................................................. 1
List of Tables ...................................................................................................................... 7
List of Figures ..................................................................................................................... 8
Abstract ............................................................................................................................. 20
1. Chapter One: Problem................................................................................................... 22
1.1. Introduction: ........................................................................................................... 22
1.1.1. Hypothesis: ..................................................................................................... 22
1.1.2. The Importance of optimizing double skin façade in hot arid climates:......... 22
1.1.3. Intentions of implementing DSF ..................................................................... 24
1.1.4.Definitions: ...................................................................................................... 26
1.1.5. Research boundaries: ...................................................................................... 26
1.1.6 Scope of work: ................................................................................................. 26
1.1.7 Thesis Structure ............................................................................................... 27
1.2. Climate characteristics of city of Riyadh, Saudi Arabia: ....................................... 27
1.2.1. Riyadh city: ..................................................................................................... 27
1.2.2. Climate description: ........................................................................................ 27
1.2.3. Solar Radiation: .............................................................................................. 30
2. Chapter Two: Background ............................................................................................ 32
2.1 Further definitions of double skin façades: ............................................................. 32
2.2. Double skin façade categories: .............................................................................. 32
2.2.1. Box-window:................................................................................................... 33
2.2.2. Shaft-Box: ....................................................................................................... 33
2.2.3. Corridor: .......................................................................................................... 34
2.2.4. Multi-Story:..................................................................................................... 35
2.3. Double skin façade influence on energy consumption: ......................................... 36
2.4. Thermal performance of double skin facades: ....................................................... 38
2.4.1. Overheating problems: .................................................................................... 39
2.4.2. Temperature of the internal wall: .................................................................... 41
2.4.3. Façade response to solar heat gain: ................................................................. 42
2.5. Ventilation and airflow types: ................................................................................ 44
2.5.1. Airflow types: ................................................................................................. 46
2.5.2. Stack effect: .................................................................................................... 48
3

2.5.3. Cavity’s heat extraction: ................................................................................. 49
2.6. Integrating HVAC system with the façade ............................................................ 49
2.7. The influence of using different glazing types: ..................................................... 51
2.8. The influence of integrating shading devices: ....................................................... 52
2.9. Case studies:........................................................................................................... 53
2.9.1. Sowwah Square, Abu Dhabi, United Arab Emirates: ..................................... 53
2.9.2. Supreme Audit Court, Tehran, Iran: ............................................................... 55
2.9.3. Capital Gate, Abu Dhabi, United Arab Emirates: ........................................... 56
2.9.4. Cleveland Clinics, Abu Dhabi, United Arab Emirates: .................................. 58
2.9.5. Arcapita Bank Headquarters, Manama, Bahrain: ........................................... 59
3. Chapter Three: Methodologies ..................................................................................... 61
3.1. Data acquisition steps: ........................................................................................... 61
3.1.1. Modeling a hypothetical building: .................................................................. 61
3.1.2. Test several variables (Preliminary studies): .................................................. 61
3.1.3. Final variables list: .......................................................................................... 62
3.2. Thermal dynamic simulation tool: ......................................................................... 62
3.3. Selected hypothetical building: .............................................................................. 63
3.4. Preliminary studies: ............................................................................................... 65
3.5. Final testing variables: ........................................................................................... 66
Installation types: ...................................................................................................... 66
Orientation: ............................................................................................................... 66
Cavity depth distance: ............................................................................................... 66
Glazing types: ........................................................................................................... 67
Shading device: ......................................................................................................... 67
Ventilation: ............................................................................................................... 67
3.6. Model settings and simulation process: ................................................................. 68
3.6.1. Modeling: ........................................................................................................ 68
3.6.2. Shading calculations: ...................................................................................... 69
3.6.3. Airflow Setting: .............................................................................................. 69
3.6.4. HVAC Layout: ................................................................................................ 72
3.6.5. Load calculations: ........................................................................................... 74
3.6.6. Final simulation: ............................................................................................. 76
3.7. Model inputs: ......................................................................................................... 77
4

3.7.1. Building construction: ..................................................................................... 77
3.7.2. Construction of double skin façade: ............................................................... 78
3.7.3. Weather data: .................................................................................................. 80
3.7.4. Shading settings: ............................................................................................. 82
3.7.5. Spaces thermal conditions and loads: ............................................................. 82
People occupant density (m
2
/person) ........................................................................ 83
Lighting sensible gain (W/m
2
) .................................................................................. 83
Computer sensible gain (W/m
2
) ................................................................................ 83
3.7.6. Occupation profile: ......................................................................................... 83
3.7.7. HVAC system layout and ventilation settings: ............................................... 84
3.8. Expected results: .................................................................................................... 86
3.8.1. Energy performance: ....................................................................................... 86
3.8.2. Thermal performance: ..................................................................................... 87
4. Chapter Four: Preliminary Studies................................................................................ 88
4.1. Preliminary testing variables: ................................................................................ 88
4.2. Explanation of the undesired variables: ................................................................. 89
4.2.1. Cavity depth: ................................................................................................... 89
4.2.2. Glazing type on the external skin: .................................................................. 90
4.2.3. Shading device location: ................................................................................. 91
5. Chapter Five: Study Results.......................................................................................... 94
5.1. Simulation models numbering: .............................................................................. 95
5.2. Total annual building energy consumption (MWh)............................................... 96
5.2.1. Baseline scenarios: .......................................................................................... 96
5.2.2. Multi-story type scenarios: ............................................................................. 97
5.2.3. Corridor type scenarios: .................................................................................. 98
5.2.4. Box-window type scenarios: ........................................................................... 99
5.3. Cooling energy ..................................................................................................... 102
5.3.1. Baseline scenarios: ........................................................................................ 102
5.3.2. Multi-story type scenarios: ........................................................................... 103
5.3.3. Corridor type scenarios: ................................................................................ 104
5.3.4. Box-window type scenarios: ......................................................................... 105
5.4. Space conditioning sensible (kW): ...................................................................... 108
5.4.1. South façade scenarios: ................................................................................. 108
5

5.4.2. North façade scenarios: ................................................................................. 110
5.4.3. East façade scenarios: ................................................................................... 111
5.4.4. West façade scenarios: .................................................................................. 112
5.5. Solar gain: ............................................................................................................ 113
5.5.1. South façade scenarios: ................................................................................. 113
5.5.2. North façade scenarios: ................................................................................. 114
5.5.3. East façade scenarios: ................................................................................... 115
5.5.4. West façade: .................................................................................................. 116
5.6. Air temperature in the cavity: .............................................................................. 117
5.6.1. South façade scenarios: ................................................................................. 117
5.6.2. North façade scenarios: ................................................................................. 118
5.6.3. East façade scenarios: ................................................................................... 119
5.6.4. West façade scenarios: .................................................................................. 120
5.7. Surface temperature: ............................................................................................ 121
5.7.1. Outer skin surface temperature: .................................................................... 121
5.7.2. Inner glass surface temperature .................................................................... 125
5.7.3. Inner wall surface temperature...................................................................... 129
5.8. Comfort in rooms adjacent to the cavity: ............................................................. 133
5.8.1. South façade scenarios: ................................................................................. 133
5.8.2. North façade scenarios: ................................................................................. 135
5.8.3. East façade scenarios: ................................................................................... 136
5.8.4. West façade scenarios: .................................................................................. 137
6. Chapter Six: Double Skin Facade Scenarios’ Perfo rmance ........................................ 138
6.1. Double skin façade installation typology performance: ...................................... 138
6.1.1. Multi-story type: ........................................................................................... 138
6.1.2. Corridor type: ................................................................................................ 143
6.1.3. Box-window type: ......................................................................................... 148
6.2. Double skin façade behavior in different orientations: ........................................ 153
6.2.1. South façade .................................................................................................. 153
6.2.2. North façade .................................................................................................. 158
6.2.3. East façade .................................................................................................... 163
6.2.4. West façade ................................................................................................... 168
6.3. Cavity depth effect: .............................................................................................. 173
6

6.3.1. 100 cm:.......................................................................................................... 173
6.3.2. 150 cm:.......................................................................................................... 178
6.4. Ventilation and airflow performance ................................................................... 183
6.4.1. Natural Ventilation........................................................................................ 183
6.4.2. Integrating HVAC system to the facade ....................................................... 188
7. Chapter Seven: Conclusions $ Future Work ............................................................... 193
7.1. Summary: ............................................................................................................. 193
7.2. Conclusions: ......................................................................................................... 194
7.3. Research limitations: ............................................................................................ 195
7.4. Future work: ......................................................................................................... 196
Bibliography ................................................................................................................... 201

7

List of Tables

Table 1 Climate data (National Meterology and Environment Center 2007) ................... 28
Table 2 Solar radiation values in Riyadh city on vertical surfaces (Al-Sanea, Zedan and
Al-Ajlan 2004) .................................................................................................................. 30
Table 3 Based on the building envelope requirement for 3611 < HDD/CDD (
o
C) < 3889
from the Saudi Building Code. ......................................................................................... 65
Table 4 Construction materials inputs .............................................................................. 77
Table 5 Glazing inputs ...................................................................................................... 77
Table 6 Zones’ internal gains summary ............................................................................ 83
Table 7 Total annual building energy consumption (MWh) and energy use intensity
(kW/m
2
) for baseline cases ............................................................................................... 96
Table 8 Total annual building energy consumption (MWh) and energy use intensity
(kW/m
2
) for multi-story type scenarios ............................................................................ 97
Table 9 Total annual building energy consumption (MWh) and energy use intensity
(kW/m
2
) for box-window type scenarios ........................................................................ 100
Table 10 Building's cooling energy for baseline scenarios ............................................. 102
Table 11 Building's cooling energy for multi-story types scenarios .............................. 103
Table 12 Building's cooling energy for corridor type scenarios ..................................... 104
Table 13 Building's cooling energy for box-window type scenarios .............................. 105

8

List of Figures

Figure 1 Distribution of electricity consumption by category of consumers 2008 in Saudi
Arabia (Ministry of Economy and Planning 2010)........................................................... 24
Figure 2 Recent image of an under-construction project (King Abdullah Financial
District) In Riyadh city Source:
http://en.wikipedia.org/wiki/File:The_king_Abdullah_Financial_District..JPG ............. 25
Figure 3 Sun path in Riyadh city - Source: Sun Path Software ........................................ 29
Figure 4 A psychometric chart for Riyadh city during very hot season (May – Aug). .... 29
Figure 5 World solar radiation map. The circle shows the location of Saudi Arabia
Source: http://cliffmass.blogspot.com/2012/03/strengthening-sun.html .......................... 31
Figure 6 Box window type (Knaack, et al. 2007) ............................................................. 33
Figure 7 Shaft-box type (Knaack, et al. 2007) .................................................................. 34
Figure 8 Corridor type (Knaack, et al. 2007) .................................................................... 35
Figure 9 Multi-story type (Knaack, et al. 2007) ............................................................... 36
Figure 10 Comparison of cooling loads of base case and selective double skin scenarios
(Hamza 2007).................................................................................................................... 38
Figure 11 Perspectives of (Zaha Hadid Architects’) building in Abu Dhabi ................... 40
Figure 12 Heat Transfer through a Single Pane of Glass (Permasteelisa Group of
Companies on the Harvard De n.d.) .................................................................................. 43
Figure 13 Heat Transfer through a Double-Skin Facade (Permasteelisa Group of
Companies on the Harvard De n.d.) .................................................................................. 44
Figure 14 Types of Double-Skin Based on Air Flow (Schiefer, et al. 2008) ................... 47
9

Figure 15 Stack effect in opened and closed cavities Source:
http://continuingeducation.construction.com/article_print.php?C=685&L=5 ................. 48
Figure 16 Double Skin Façade as an exhaust duct. (H. Poirazis 2004) ............................ 50
Figure 17 Double Skin Façade as a duct for the ventilation (H. Poirazis 2004)............... 51
Figure 18 Sowwah Square buildings, ............................................................................... 53
Figure 19 double skin facade system in Sowwah project Source:
http://www.gpchicago.com/users/news_view.asp?FolderID=1829&NewsID=73 .......... 55
Figure 20 On the left: Supreme Audit Court. On the right: a cross section of the building
........................................................................................................................................... 56
Figure 21 On the right: the Capital Gate Tower. On the left: close up picture showing the
two skins on the upper part of the tower. .......................................................................... 57
Figure 22 the double-skin facade system in the Capital Gate Tower (Schofield 2012) ... 57
Figure 23 an interior shot of the double skin facade for the upper floors of the tower .... 58
Figure 24 On the right: Cleveland Clinic, Abu Dhabi, UAE (Jordana 2012). On the left:
Cleveland Clinic’ double skin façade configuration (Fortmeyer 2009) ........................... 59
Figure 25 Arcapita Bank HQ ............................................................................................ 60
Figure 26 CFD studies for the cavity of Aracbita Bank double skin façade. (T.C Chan
Center n.d.)........................................................................................................................ 60
Figure 27 Methodolgy and workflow .............................................................................. 62
Figure 28 Building layout ................................................................................................. 64
Figure 29 Final varaibles list............................................................................................ 68
Figure 30 example of a modeled scenario ........................................................................ 69
Figure 31 A result of SunCast simulation to calculate solar shading ............................... 69
10

Figure 32 Assigning the openings in Macroflo................................................................. 70
Figure 33 Closed openings................................................................................................ 71
Figure 34 Volume flow in the cavity ................................................................................ 72
Figure 35 Single skin façade and double skin façade (Naturally ventilated cavity) HVAC
layouts ............................................................................................................................... 73
Figure 36 Double skin façade (mechanically ventilated cavity) HVAC layout ............... 73
Figure 37 An example of a summary report of building heating and cooling performance
........................................................................................................................................... 74
Figure 38 Assigning flow rate for each zone based on the generated report .................... 75
Figure 39 Example of the simulation window .................................................................. 76
Figure 40 Multi-story type ................................................................................................ 78
Figure 41 Corridor Type ................................................................................................... 79
Figure 42 Box-window type ............................................................................................. 80
Figure 43 Riyadh's weather data ....................................................................................... 80
Figure 44 Acquired data from the U.S. Department of Energy including monthly dry bulb
temperatures and solar radiarion. ...................................................................................... 81
Figure 45 Thermal conditions settings window ................................................................ 82
Figure 46 Daily occupation profile ................................................................................... 84
Figure 47 HVAC system for the single skin façade and the naturally ventilated cavity .. 84
Figure 48 System layout for mechanically ventilated multi-story type cavity ................. 85
Figure 49 System layout for mechanically ventilated corridor type cavity ...................... 85
Figure 50 System layout for mechanically ventilated box-window type cavity ............... 85
Figure 51 The main three examined scenarios ................................................................. 86
11

Figure 52 The variables list (the highlighted are the cancelled variables) ....................... 88
Figure 53 Inner glass temperature in peak day for three cavities' depths for east facing
cavity ................................................................................................................................. 89
Figure 54 Energy use intensity (kWh/m2) for different cavity depths for cavity facing
east .................................................................................................................................... 90
Figure 55 Inner glazing surface temperature for two glazing types scenarios on the
external skin ...................................................................................................................... 91
Figure 56 Cavity’s air temperature in peak day for two shading locations scenarios facing
east .................................................................................................................................... 92
Figure 57 Inner glass temperature in peak day for two shading locations scenarios facing
east .................................................................................................................................... 93
Figure 58 Total annual building energy consumption (MWh) for baseline cases ........... 96
Figure 59 Total annual building energy consumption (MWh) for for multi-story type
scenaios ............................................................................................................................. 98
Figure 60 Total annual building energy consumption (MWh) and energy use intensity
(kW/m
2
) for corridor type scenarios ................................................................................. 98
Figure 61 Total annual building energy consumption (MWh) for corridor type scenarios
........................................................................................................................................... 99
Figure 62 Total annual building energy consumption (MWh) for box-window type
scenarios .......................................................................................................................... 100
Figure 63 Total annual building energy consumption (MWh) for all scenarios............. 101
Figure 64 Building's cooling energy/m
2
for baseline scenarios ...................................... 102
Figure 65 Building's cooling energy/m
2
for multi-story type scenarios ......................... 103
12

Figure 66 Building's cooling ebergy/m
2
for corridor type scenarios .............................. 104
Figure 67 Building's cooling energy/m
2
for box-window scenarios .............................. 106
Figure 68 Cooling energy for all of the scenarios ........................................................... 107
Figure 69 Space conditioning sensible (kW) for south facing spaces in the peak day (6
th

of August) ....................................................................................................................... 108
Figure 70 Space conditioning sensible (kW) for north facing spaces in the peak day (6th
of August) ....................................................................................................................... 110
Figure 71 Space conditioning sensible (kW) for east facing spaces in the peak day (6th of
August) ............................................................................................................................ 111
Figure 72 Space conditioning sensible (kW) for west facing spaces in the peak day (6th
of August) ....................................................................................................................... 112
Figure 73 Solar gain (kW) in south facing spaces in the peak day (6th of August) ....... 113
Figure 74 Solar gain (kW) in north facing spaces in the peak day (6th of August) ....... 114
Figure 75 Solar gain (kW) in east facing spaces in the peak day (6th of August) .......... 115
Figure 76 Solar gain (kW) in west facing spaces in the peak day (6th of August) ........ 116
Figure 77 Air temperature in south facing cavities in the peak day (6th of August) ...... 117
Figure 78 Air temperature in north facing cavities in the peak day (6th of August) ...... 118
Figure 79 Air temperature in east facing cavities the peak day (6th of August) ............ 119
Figure 80 Air temperature in west facing cavities the peak day (6th of August) ........... 120
Figure 81 Outer skin temperature for south facing cavities in the peak day (6th of August)
......................................................................................................................................... 121
Figure 82 Outer skin temperature for north facing cavities in the peak day (6th of August)
......................................................................................................................................... 122
13

Figure 83 Outer skin temperature for east facing cavities in the peak day (6th of August)
......................................................................................................................................... 123
Figure 84 Outer skin temperature for west facing cavities in the peak day (6th of August)
......................................................................................................................................... 124
Figure 85 Inner skin (glass) temperature for south facing cavities in the peak day (6th of
August) ............................................................................................................................ 125
Figure 86 Inner skin (glass) temperature for north facing cavities in the peak day (6th of
August) ............................................................................................................................ 126
Figure 87 Inner skin (glass) temperature for east facing cavities in the peak day (6
th
of
August) ............................................................................................................................ 127
Figure 88 Inner skin (glass) temperature for west facing cavities in the peak day (6
th
of
August) ............................................................................................................................ 128
Figure 89 Inner skin (wall) temperature for south facing cavities in the peak day (6
th
of
August) ............................................................................................................................ 129
Figure 90 Inner skin (wall) temperature for north facing cavities in the peak day (6
th
of
August) ............................................................................................................................ 130
Figure 91 Inner skin (wall) temperature for east facing cavities in the peak day (6
th
of
August) ............................................................................................................................ 131
Figure 92 Inner skin (wall) temperature for west facing cavities in the peak day (6
th
of
August) ............................................................................................................................ 132
Figure 93 predicted percentage of dissatisfied occupants for spaces facing south in the
peak day (6
th
of August) .................................................................................................. 133
14

Figure 94 predicted percentage of dissatisfied occupants for spaces facing north in the
peak day (6
th
of August) .................................................................................................. 135
Figure 95 predicted percentage of dissatisfied occupants for spaces facing east in the peak
day (6
th
of August) .......................................................................................................... 136
Figure 96 predicted percentage of dissatisfied occupants for spaces facing west in the
peak day (6
th
of August) .................................................................................................. 137
Figure 97 Space conditioning sensible (kW) for scenario 025-m-w-100-rc-ex-m and
baseline cases in the peak day (6
th
of August) ................................................................ 139
Figure 98 Solar gain (kW) for scenario 025-m-w-100-rc-ex-m and baseline cases in the
peak day (6th of August)................................................................................................. 140
Figure 99 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 025-m-w-
100-rc-ex-m (right) ......................................................................................................... 140
Figure 100 Thermal performance for scenario 013-m-s-100-rc-ex-m, measuring inner
skin (glass) surface temperature in comparison to baseline cases in peak day (6th of
August) ............................................................................................................................ 142
Figure 101 Space conditioning sensible (kW) for scenario 052-c-w-150-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 144
Figure 102 Solar gain (kW) for scenario 052-c-w-150-rc-ex-m and baseline cases in peak
day (6th of August) ......................................................................................................... 145
Figure 103 Figure 69 Solar gain and space conditioning sensible (in the peak day)
comparison between baseline case (left), baseline case with shading (center), and
scenario 052-m-w-150-rc-ex-m (right) ........................................................................... 145
15

Figure 104 Thermal performance for scenario 034-c-n-150-rc-ex-m, measuring inner skin
(glass) surface temperature in comparison to baseline cases in peak day (6th of August)
......................................................................................................................................... 147
Figure 105 Space conditioning sensible (kW) for scenario 076-b-w-150-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 149
Figure 106 Solar gain (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in peak
day (6th of August) ......................................................................................................... 150
Figure 107 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 076-b-w-
150-rc-ex-m (right) ......................................................................................................... 150
Figure 108 Thermal performance for scenario 058-b-n-150-rc-ex-m, measuring inner
skin (glass) surface temperature in comparison to baseline cases in peak day (6th of
August) ............................................................................................................................ 152
Figure 109 Space conditioning sensible (kW) for scenario 064-b-s-150-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 154
Figure 110 Solar gain (kW) for scenario 064-b-s-150-rc-ex-m and baseline cases in peak
day (6th of August) ......................................................................................................... 155
Figure 111 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 064-b-s-
150-rc-ex-m (right) ......................................................................................................... 155
Figure 112 Thermal performance for scenario 061-b-s-100-rc-ex-m, measuring inner skin
(glass) surface temperature in comparison to baseline cases in peak day (6th of August)
......................................................................................................................................... 157
16

Figure 113 Space conditioning sensible (kW) for scenario 058-b-n-150-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 159
Figure 114 Solar gain (kW) for scenario 058-b-n-150-rc-ex-m and baseline cases in the
peak day (6th of August)................................................................................................. 160
Figure 115 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 058-b-n-
150-rc-ex-m (right) ......................................................................................................... 160
Figure 116 Thermal performance for scenario 058-b-n-150-rc-ex-m, measuring inner skin
(glass) surface temperature in comparison to baseline cases in peak day (6th of August)
......................................................................................................................................... 162
Figure 117 Space conditioning sensible (kW) for scenario 070-b-e-150-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 164
Figure 118 Solar gain (kW) for scenario 070-b-e-150-rc-ex-m and baseline cases in the
peak day (6th of August)................................................................................................. 165
Figure 119 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 070-b-e-
150-rc-ex-m (right) ......................................................................................................... 165
Figure 120 Thermal performance for scenario 070-b-e-150-rc-ex-m, measuring inner skin
(glass) surface temperature in comparison to baseline cases in peak day (6th of August)
......................................................................................................................................... 167
Figure 121 Space conditioning sensible (kW) for scenario 076-b-w-150-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 169
17

Figure 122 Solar gain (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in the
peak day (6th of August)................................................................................................. 170
Figure 123 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 076-b-w-
150-rc-ex-m (right) ......................................................................................................... 170
Figure 124 Thermal performance for scenario 076-b-w-150-rc-ex-m, measuring inner
skin (glass) surface temperature in comparison to baseline cases in peak day (6th of
August) ............................................................................................................................ 172
Figure 125 Space conditioning sensible (kW) for scenario 073-b-w-100-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 174
Figure 126 Solar gain (kW) for scenario 073-b-w-100-rc-ex-m and baseline cases in the
peak day (6th of August)................................................................................................. 175
Figure 127 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 073-b-w-
100-rc-ex-m (right) ......................................................................................................... 175
Figure 128 Thermal performance for scenario 061-b-s-100-rc-ex-m, measuring inner skin
(glass) surface temperature in comparison to baseline cases in peak day (6th of August)
......................................................................................................................................... 177
Figure 129 Space conditioning sensible (kW) for scenario 076-b-w-150-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 179
Figure 130 Solar gain (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in the
peak day (6th of August)................................................................................................. 180
18

Figure 131 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 076-b-w-
150-rc-ex-m (right) ......................................................................................................... 180
Figure 132 Thermal performance for scenario 058-b-n-150-rc-ex-m, measuring inner skin
(glass) surface temperature in comparison to baseline cases in peak day (6th of August)
......................................................................................................................................... 182
Figure 133 Space conditioning sensible (kW) for scenario 075-b-w-150-rc-ex-n and
baseline cases in peak day (6th of August) ..................................................................... 184
Figure 134 Solar gain (kW) for scenario 075-b-w-150-rc-ex-m and baseline cases in the
peak day (6th of August)................................................................................................. 185
Figure 135 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 075-b-w-
150-rc-ex-m (right) ......................................................................................................... 185
Figure 136 Thermal performance for scenario 057-b-n-150-rc-ex-n, measuring inner skin
(glass) surface temperature in comparison to baseline cases in peak day (6th of August)
......................................................................................................................................... 187
Figure 137 Space conditioning sensible (kW) for scenario 076-b-w-150-rc-ex-m and
baseline cases in peak day (6th of August) ..................................................................... 189
Figure 138 Solar gain (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in the
peak day (6th of August)................................................................................................. 190
Figure 139 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 076-b-w-
150-rc-ex-m (right) ......................................................................................................... 190
19

Figure 140 Thermal performance for scenario 058-b-n-150-rc-ex-m, measuring inner skin
(glass) surface temperature in comparison to baseline cases in peak day (6th of August)
......................................................................................................................................... 192

20

Abstract

Due to the vast development in construction in hot-arid climate areas,
implementing innovative façade technologies is crucial to meet owners and developer
needs, and to meet climate conditions requirements. Buildings are major contributors of
energy consumption due to the high glazing areas and their role of increasing cooling
demand. Double skin facades are used in cold and temperate climates to reduce heating
loads and for other benefits; however, it’s believed that a double skin façade can reduce
cooling loads in hot-arid climates. This research project aims to find optimized
configurations for double skin façades in this climate. Therefore, by implementing fully
glazed double skin façades in hot-arid climate areas with careful design, buildings’
energy consumption can be reduced by greater than 10% compared to a single skin
façade with high glazing area. Dynamic thermal analysis using IES-VE has been
performed on a hypothetical office building in Riyadh city, Saudi Arabia, to simulate
baseline and double skin scenarios to examine the performance of proposed variables.
Variables include double skin façade typologies: Multi-story, corridor, and box-window,
orientation of the façade, cavity depths: 100cm and 150cm, and ventilation type inside
the cavity: natural and mechanical. Results showed that rooms adjacent to cavities in
different scenarios have lower solar gain, lower cooling load, and improved surface
temperature compared to the same rooms in baseline cases. Based on the findings, double
skin façades that can reduce energy consumption provide improved thermal performance
and help to increase comfort levels. All double skin façade scenarios showed improved
performance comparing to the baseline cases. Box-window types show substantial
21

improvement over all other scenarios. And scenarios with mechanically ventilated
cavities provided the most improved results in terms of energy and thermal performance.

22

1. Chapter One: Problem
1.1. Introduction:
A double skin façade is an envelope technology designed and improved in Europe and
cold climates to save energy on heating and to enhance indoor comfort in a building.
Lately, several buildings around the world in cold and moderate climates have used this
technology to enhance thermal performance, provide better day lighting, natural
ventilation, noise reduction, and to add an esthetic value. However, it is difficult to find
applications of double skin façades in hot arid climates. This thesis project will analyze
and model different double skin façade typologies to test and find an optimized assembly
thermally performing to provide additional protection from the climate conditions to fully
glazed midrise office buildings in hot arid climates.

1.1.1. Hypothesis:
By implementing optimized fully glazed double skin facades in hot arid climates we can
reduce by more than 10% the cooling loads and energy consumption of fully glazed
single skin façade.

1.1.2. The Importance of optimizing double skin façade in hot arid climates:
A building envelope in a hot arid climate is exposed to harsh environment through most
of the year, which lead to the consumption of an enormous amount of energy to run
mechanical equipment to bring internal temperatures to the comfort zone. Therefore, it is
23

important to find appropriate solutions to reduce cooling loads by reducing heat gain,
lowering conditioned air loss, and to maintaining proper daylight in internal spaces.
Many countries in hot climate regions are consuming proportionally more energy in the
building sector to run HVAC system to provide comfort. Recently, there have been
increased discussions and reports regarding the energy consumption in countries like
Saudi Arabia. According to (Daya and El Baltaji 2012) Citigroup’s report, Saudi Arabia,
which is one of the major crude exporters in the world, is going to become oil importer in
2030 “ If Saudi Arabian oil consumption grows in line with peak power demand, the
country could be a net oil importer by 2030,” Heidy Rehman, an analyst at the bank,
wrote. Regardless of the accuracy of this report, it is an indisputable that the energy
demand in Saudi Arabia is becoming higher.
According to Saudi Arabia’s ninth national development plan report (Ministry of
Economy and Planning 2010, 580-596), the electricity peak load was about 38 thousand
MW in 2008, up from about 28.6 thousand MW in 2004, with an average annual growth
rate of 7.4%. The report indicates that governmental and commercial buildings, which are
the focus of this research, consume 23% of the total electricity consumption.
24

Figure 1 Distribution of electricity consumption by category of consumers 2008 in Saudi Arabia
(Ministry of Economy and Planning 2010)
Therefore, to meet with this increasing demand, it became more important to review the
current buildings’ conditions (in part since they are designed with high glazing areas)
(Fig. 2), apply sustainable methods, and examine the use of advanced technologies like
double skin facades to provide extra protection from the climate conditions.
Several research papers demonstrate that double skin façade can reduce operational
cooling loads. A comparative study (Hamza 2007) between double and single skin
facades in Cairo concluded that double skin façades can achieve good energy
performance by using proper glass properties. Therefore, applying an optimized double
skin façade might reduce cooling loads and mitigate energy issues.

1.1.3. Intentions of implementing DSF
Developing countries in hot arid climates like Saudi Arabia are experiencing substantial
development in the construction sector since the population and urbanization growth are
25

vastly increasing. Owners and developers want to apply large glass areas on their office
buildings to get the advantages of its aesthetic value, daylight and to increase the
transparency to meet with the globalization of architecture even though the large glass
area conflicts with the climate conditions. Many architects have utilized different
innovative strategies to meet the clients’ requirements and to provide protection to these
facades such as: intelligent building applications like dynamic shading devices, additional
screen layers and others. However, some of these strategies are limiting the visual
connection that glass provides. Regardless of the cost and maintenance issues, double
skin façades can provide the clients’ requirements in addition to the protectio n from the
environmental issues because it acts as a thermal buffer zone because it adds one more
transparent layer.

Figure 2 Recent image of an under-construction project (King Abdullah Financial District) In
Riyadh city Source: http://en.wikipedia.org/wiki/File:The_king_Abdullah_Financial_District..JPG

26

1.1.4.Definitions:
1.1.4.1. Double skin façade:
Double skin façade has been defined in many different ways. For this research, a double
skin façade is a combination of adding an extra external layer of glazing to the main
façade to provide the building with ventilation and sound insulation. The system
components may be designed in several ways, based on the functions desired and the
requirements. (Knaack, et al. 2007)
1.1.4.2 Cavity:
The cavity is the space that separates the two glazing layers of the double skin façade. It
acts as a buffer zone that provides a thermal and acoustic insulation. It can be accessed to
do maintenance and cleaning works. It can be either naturally or mechanically ventilated.
The distance between the two skins varies from 20cm to 2m. This space can be used to
integrate shading devices to provide more protection.

1.1.5. Research boundaries:
This thesis is going to examine the thermal performance and energy consumption
for typical office buildings in hot-arid climates. The work will not include
explorations of daylight, cost, aesthetics, and acoustics.

1.1.6 Scope of work:
This research project is examining different design configurations and solutions
based on several variables and components to find out best design strategies for
27

double skin façade. This thesis will result in a design guideline. Hypothetical
office building digital models for a single glazed building and double skin
building scenarios are going to be examined and simulated in Riyadh city in Saudi
Arabia.

1.1.7 Thesis Structure
This thesis consists of an introduction, background research, methodologies,
preliminary studies, simulation results, double skin façade scenario’s
performance, conclusions and future work.

1.2. Climate characteristics of city of Riyadh, Saudi Arabia:
1.2.1. Riyadh city:
Riyadh is the capital city of the Kingdom of Saudi Arabia located on latitude
24.7N and longitude 46.73E, it houses more than 4.9 million (ArRiyadh 2011).

1.2.2. Climate description:
Summer temperatures in Riyadh are very hot, with noticeable fluctuation in high
and low temperature during the day especially in summer. In summer, low
temperatures are ranging between (30
o
C – 37
o
C) and high temperatures are
ranging between (45
o
C – 52
o
C). The average high temperature in July is 43.5°C.
Winters are mild with cold windy nights; high temperatures are ranging between
28

(20
o
C - 5
o
C). The overall climate is arid; humidity percentage in summer is
around 19% and 50% in winter. Riyadh receives little rainfall between November
and May (Table 1). It is also known to have many dust storms during the spring
and the summer. The dust is regularly thick that visibility is less than 10 meters.
(Wikipedia 2012 )

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Record high °C 31.5 34.8 38 42 45.1 49.8 52 47.8 44.5 41 36 31 52
Average high °C 20.1 23 27.6 34 39.6 42.7 43.4 43.2 41.3 35.1 27.6 22 33.1
Daily mean °C 14.4 16.9 21.1 26.9 32.9 35.4 36.6 36.5 33.3 28.2 21.4 16.1 26.6
Average low °C 6.9 9 15 20.3 25.7 27.6 29.1 28.8 25.7 20.9 15.3 8.4 19.9
Record low °C -1 0.5 4.5 11 18 21 23.6 22.7 16.1 13 7 1.4 -1
Rainfall mm 11.7 8.5 24.7 22.3 4.6 0 0 0.2 0 1.7 7.9 13 94.6
% humidity 47 38 34 28 17 11 10 12 14 21 36 47 26
Avg. precipitation
days
5.8 4.8 9.8 10 3.5 0 0.2 0.2 0 1.2 3.4 6.3 45.2

Table 1 Climate data (National Meterology and Environment Center 2007)

29

Figure 3 Sun path in Riyadh city - Source: Sun Path Software

Figure 4 A psychometric chart for Riyadh city during very hot season (May – Aug).
30

1.2.3. Solar Radiation:
Solar radiation in Riyadh is intense and considered one of the highest among the
world (Figure 5) according to (Al-Sanea, Zedan and Al-Ajlan 2004) who has
modified ASHRAE data for Riyadh solar radiation in a research paper published
in 2004 (Table 2).

Table 2 Solar radiation values in Riyadh city on vertical surfaces (Al-Sanea, Zedan and Al-Ajlan
2004)

High solar radiation has a significant impact on the performance and the
configuration of double skin façade. (Compagno 2002) has described how to
prevent overheating effect in the cavity when solar radiation is high as in Riyadh
case by considering the width of the cavity and the size of the ventilation
openings. “When solar radiation is high, the façade cavity has to be well
31

ventilated, to prevent overheating. The key criteria here are the width of the
cavity and the size of the ventilation openings in the outer skin. The air change
between the environment and the cavity is dependent on the wind pressure
conditions on the building’s skin, the stack effect and the discharge coefficient of
the openings. These vents can either be left open all the time (passive systems), or
opened by hand or by machine (active system). Active systems are very
complicated and therefore expensive in terms of construction and maintenance.”

Figure 5 World solar radiation map. The circle shows the location of Saudi Arabia
Source: http://cliffmass.blogspot.com/2012/03/strengthening-sun.html

32

2. Chapter Two: Background
2.1 Further definitions of double skin façades:
(Wigginton and Harris 2002) described the double skin façade system as “an external
glass surface, a shading system, a gap filled with air and an insulating double internal
glazing system, sometimes integrated with opaque walls”.
(Boake 2003) defined the double skin facade as “essentially a pair of glass “skins”
separated by an air corridor. The main layer of glass is usually insulating. The air space
between the layers of glass acts as insulation against temperature extremes, winds, and
sound. Sun-shading devices are often located between the two skins. All elements can be
arranged differently into numbers of permutations and combinations of both solid and
diaphanous membranes”.
Also, (Uuttu 2001) defines the double skin facade as “a pair of glass skins separated by
an air corridor (also called cavity or intermediate space) ranging in width from 20 cm to
several meters. The glass skins may stretch over an entire structure or a portion of it. The
main layer of glass, usually insulating, serves as part of a conventional structural wall or
a curtain wall, while the additional layer, usually single glazing, is placed either in front
of or behind the main glazing. The layers make the air space between them work to the
building’s advantage primarily as insulation against temperature extremes and sound.”

2.2. Double skin façade categories:
According to (Knaack, et al. 2007), (Oesterle 2001) and (Aksamija 2009) , the
main four typologies for double skin façade and their description are:

33

2.2.1. Box-window:
The closed box is partitioned as one unit for each floor. Each box in enclosed horizontally
and vertically and has its own air circulation. For ventilation, it has two vents on the
external leaf to allow the ingress of fresh air and the egress of the cavity air (Figure 6).

Figure 6 Box window type (Knaack, et al. 2007)

2.2.2. Shaft-Box:
The shaft box (Figure 7) is a different version of box-window type; however, it extracts
the air from its own cavity into special adjacent shafts that extend over several stories in
order to create a stack effect.
34

Figure 7 Shaft-box type (Knaack, et al. 2007)
2.2.3. Corridor:
The corridor type is partitioned at each floor level or may extend over each several floors.
In the context of ventilation, air vents on the external skin should be located near the
floor and the ceiling for each level. Natural, mechanical and hybrid are three possible
ventilation types. (Figure 8)
35

Figure 8 Corridor type (Knaack, et al. 2007)
2.2.4. Multi-Story:
The cavity space between the inner and the outer skins extends over the entire façade or
for some cases by a number of rooms and floors without any dividers. The vents openings
for the air-intake and extraction of the cavity are located near the ground and the roof
with large sizes. According to (Oesterle 2001) “the rooms behind the multistory facades
have to be mechanically ventilated, and the façade can be used as a joint air duct for this
purpose.” (Figure 9)
36

Figure 9 Multi-story type (Knaack, et al. 2007)

2.3. Double skin façade influence on energy consumption:
Much background research has been conducted to examine double skin facades in cold
and moderate climates; however, only a little tested the influence of double skin façade in
hot arid climates. Fundamentally, a double skin façade is capable to reduce the energy
consumption by minimizing direct solar radiation which leads to reduce the cooling loads
by carful design for its components (H. Poirazis 2004).
According to (Arons 2000)“energy savings attributed to Double Skin Facades are
achieved by minimizing solar loading at the perimeter of buildings. Providing low solar
factor and low U Value minimizes cooling load of adjacent spaces”.
37

The external skin can provide thermal insulation both in summer and winter. Creating a
buffer zone in the cavity can result in a considerable energy consumption reduction.
(Oesterle 2001)
(Saelens, Carmeliet and Hens 2003) have analyzed the energy performance of three
multistory facades used in a single office. The authors concluded that it is possible to
achieve improvement in energy saving by using double skin facades. Moreover, the
authors indicated that the energy performance relies on the cavity air performance.
(Hamza 2007) has published in Energy and Buildings vol. 40 a research paper to compare
cooling loads on a single skin façade and a double skin façade with different
configurations. The author tested three possible changes to the physical properties of the
external layer of the double skin façade using IES-VE software. The tested model is a six
stories building located in Cairo, Egypt. The double skin façade type is a multistory with
1 meter cavity width. The author tested three different glass properties on the external
skin: clear, tinted and reflective, (Figure 10). She concluded that Double skin façade
technology is suitable for reducing air conditioning loads in hot arid climates. Moreover,
she stated: “Using lower shading co -efficient and g-value than transparent glass on the
external leaf of the double skin facade offers a first line of defense against the onslaught
of the direct solar radiation in hot arid climates.”

38

Figure 10 Comparison of cooling loads of base case and selective double skin scenarios (Hamza 2007)

2.4. Thermal performance of double skin facades:
(Soberg 2008) described the function of the double skin façade as a thermal buffer zone
against the external environment whether it is a cold or hot. “ A double skin for a desert
climate is fundamentally different than the version more commonly implemented in
cooler, northern regions. While both systems rely on creating a cavity of air that cushions
the interior from the exterior, a cool-region system is designed to minimize the heat loss
from the interior spaces and relies on the increased temperature of the cavity air to do
so. In the UAE, however, the opposite is true and the air cavity is called upon to minimize
the radiant heat gain from the exterior to the interior occupied zones.”
According to (Uuttu 2001) an opened multistory double skin façade can prevent
overheating in the cavity which can reduce the cooling loads and mitigate the temperature
39

inside the cavity. Uuttu described the behavior of this type of façade that the accumulated
air at the top of the cavity becomes warmer. Openings located on the top will extract the
hot air and replace it with cooler air from bottom openings.
(Poirazis and Rosenfeld 2003) conducted a study for four types of double skin façade
with different variables include seasons (summer and winter), with and without shading,
naturally and mechanically ventilation for the cavity and two different vents sizes for
natural ventilation. . The study calculated by two computing programs (WIS and
MathCAD). In general, the author concluded that the double skin façade’s U-value and
the energy transmitted to the ventilation air decreased when the shading is located inside
the cavity. The values increased slightly in the summer. The highest transmitted energy to
the air is when the cavity depth is 800 cm, and the lowest when it is 50 cm.
In general, air is preferred to flow inside the cavity to extract heat that accumulated in the
cavity. The air flow is able to mitigate the temperature inside the cavity which would
reduce conduction, convection, and radiation from and to the adjacent spaces. Therefore,
less cooling energy is required. (Arons 2000)
2.4.1. Overheating problems:
The design of a double skin façade can affect the cavity by increasing the temperature
and causing overheating problems in the cavity, which would lead to increase the cooling
loads and discomfort for the adjacent spaces to the cavity.
To avoid overheating, the design has to consider several components such as the
ventilation, the depth of the cavity and the shading. (Jager 2008) claims that the minimum
40

depth of the intermediate space should be more than 20 cm . (Compagno 2002) agrees
that the depth of the cavity would influence the overheating effect in addition to the size
of the vents.
A study by (Yagoub, Appleton and Stevens 2010) to analyze the thermal performance on
a proposed building (
Figure 11) that has a double skin façade in Abu Dhabi found out that the cavity based on
the simulation is overheated because of the intense climate conditions and the
components of the design.

Figure 11 Perspectives of (Zaha Hadid Architects’) building in Abu Dhabi

41

The building is designed by Zaha Hadid Architects and comprises 17 floors with a single
glazed outer skin and double glazed for the inner skin and integrated motorized shading
devices to reduce the solar gains be.
The study analyzed the performance by running a dynamic thermal simulation. IES-VE
software was used to model and analyze the cavity with depth of 60 cm – 80 cm.
The author claimed that the analysis showed that the air temperature in the double skin
façade cavity would reach over 70 °C, which will not be optimal for the motors of the
shading devices in the cavity. Also, high temperatures of the internal glazing could result
in uncomfortable indoor conditions especially for the spaces adjacent to the cavity. In
general, the author concluded that the simulations results need to be validated. However,
the building is capable to achieve comfortable internal conditions, if some effective
ventilation used in the cavity, even though it is predicted that the building will consume
more energy to mitigate the cavity temperature in the climate of Abu Dhabi.

2.4.2. Temperature of the internal wall:
The double skin façade is claimed to have a low thermal transmission U-value and low
solar heat gain coefficient (G-value) (Kragh 2000). It is essential, during the summer
season, to design the system to decrease the solar gain and the air temperature inside the
cavity so the internal surface temperature would be decreased; thus, reduction in cooling
loads.
42

Proper combination of double skin façade’s type and geometry, size of openings, type
and positioning of shading devices and pane types can provide improved building
performance.

2.4.3. Façade response to solar heat gain:

Since solar radiation is composed of long-waves and short-waves, it is essential to
understand how the building envelope would respond to different wave lengths. A
general rule is that long wave lengths carry lower energy. (Permasteelisa Group of
Companies on the Harvard De n.d.)
Clear glass is transparent to high frequency solar radiation (short waves), but almost
opaque to low frequency radiation (long waves). Once the solar heat energy passes into
the glazing, the glass absorbs the energy and will become a heat radiator. The radiated
heat is a long wave radiation; therefore, it will be trapped in the cavity and raise the
temperature. (Figure 12). To avoid solar heat gain from accessing the cavity or reaching
the internal surface, shading devices. Whether they are located on the external skin or
inside the cavity, can play a role in absorbing and controlling the solar radiation. The
shading device can reflect part of the high frequency radiation (short wave) back through
the outer skin and absorbs the rest of it and convect and re-radiate it back in the cavity as
a low frequency heat. Thus, there is lower heat gain on the inner skin since the clear glass
(inner skin’s glass) is a barrier to low frequency radiation. Consequently, lower cooling
43

loads and also, exhaust air from the adjacent rooms can extract the accumulated air in the
cavity. (Figure 13)

Figure 12 Heat Transfer through a Single Pane of Glass (Permasteelisa Group of Companies on the
Harvard De n.d.)
44

Figure 13 Heat Transfer through a Double-Skin Facade (Permasteelisa Group of Companies on the
Harvard De n.d.)

2.5. Ventilation and airflow types:

Ventilation is one of the most significant components of a double skin façade system. It
helps to decrease the air temperature in the cavity and to extract undesired hot air.
However, it is important to integrate other components such as the pane types and the
type and location of shading devices to avoid overheating in the cavity and thus
increasing the cooling loads. The type of the double skin façade and the width and height
of the intermediate space in addition to the type of the airflow would have a significant
effect on the temperature of the air. (H. Poirazis 2004).
The main ventilation types in the cavity use different sources of ventilation; (Kragh 2000)
categorizes the double skin facades based on the cavity ventilation system in three types:
45

Naturally Ventilated Wall: “An extra skin is added to the outside of the building
envelope. In periods with no solar radiation, the extra skin provides additional
thermal insulation. In periods with solar irradiation, the skin is naturally ventilated
from/to the outside by buoyancy (stack) effects - i.e. the air in the cavity rises
when heated by the sun (the solar radiation must be absorbed by blinds in the
cavity). Solar heat gains are reduced as the warm air is expelled to the outside.
The temperature difference between the outside air and the heated air in the cavity
must be significant for the system to work. Thus, this type of façade cannot be
recommended for hot climates”.
Active Wall: “An extra skin is applied to the inside of the building envelope;
inside return air is passing through the cavity of the façade and returning to the
ventilation system. In periods with solar radiation the energy, which is absorbed
by the blinds, is removed by ventilation. In periods with heating loads, solar
energy can be recovered by means of heat exchangers. Both during cold periods
with no or little solar irradiation and during periods with solar gains or cooling
loads, the surface temperature of the inner glass is kept close to room temperature,
leading to increased occupant comfort in the perimeter zone, near the façade. This
type of façade is recommended for cold climates, because of the increased
comfort during the cold season and the possible recovery of solar energy”.
Interactive Wall: “The principle of the interactive wall is much like that of the
naturally ventilated wall with the significant difference that the ventilation is
forced. This means that the system works in situations with high ambient
temperatures, as it does not depend on the stack effect alone. The system is thus
46

ideal for hot climates with high cooling loads. During cold periods with no solar
irradiation (e.g. during night-time) the ventilation can be minimized for increased
thermal insulation. Apart from the advantages in terms of solar and thermal
performance the system allows the use of operable windows for natural
ventilation, even in high-rise buildings”.

According to (Aksamija 2009), selection of the cavity ventilation type should be based on
the location of the building. Natural ventilation is suitable for temperate and cold
climates. Mechanical ventilation is more suitable for extreme climate, like the hot-arid
areas. Hybrid systems can be used in climates that allow this combination where natural
ventilation used in heating periods and mechanical ventilation used in cooling periods.

2.5.1. Airflow types:
A technical report by (Schiefer, et al. 2008) classified airflow types (Figure 14) inside the
cavity to five main types based on the origin and the destination of the air as the
following:
1. Outdoor air curtain
In this type, the air inside the cavity comes from the outside and is immediately
exhausted back to the outside without interacting with the building’s ventilation systems.
2. Indoor air curtain
47

Unlike the outdoor air curtain, the air inside the cavity comes from the inside of the
adjoining room and is returned back to the room.
3. Air supply
In this type, the air source of the cavity and the adjoining room is the outdoor air. This air
is brought to the inside of the adjoining room through the cavity.
4. Air exhaust
The air in the cavity comes from the inside of the room and is exhausted to the outside.
5. Buffer zone
In this type, the cavity is not ventilated which forms a buffer zone between the inside and
the outside.

Figure 14 Types of Double-Skin Based on Air Flow (Schiefer, et al. 2008)

48

2.5.2. Stack effect:
The stack effect is the physical effect that can cause air circulation and heat extraction. It
basically caused by two factors: differences in air temperature and differences in air
pressure. (Figure 15)
Natural ventilation or injecting exhaust air into the cavity from the HVAC system can
help to replace the warm air in the cavity with cooler air as a result of stack effect that
rises the warm air up and extract it through vents. (Lee, et al. 2002) described the
behavior of the stack effect: “ as re-radiation from absorbed radiation is emitted into the
intermediate cavity, a natural stack effect results, which causes the air to rise, taking with
it additional heat”

Figure 15 Stack effect in opened and closed cavities
Source: http://continuingeducation.construction.com/article_print.php?C=685&L=5
49

2.5.3. Cavity’s heat extraction:
Lee (Lee, et al. 2002) claims that the heat extraction in the cavity relies on the integrated
sun shading in cavity to control loads. The author stated: “The concept is similar to
exterior shading systems in that solar radiation loads are blocked before entering the
building, except that heat absorbed by the between-pane shading system is released
within the intermediate space, then drawn off through the exterior skin by natural or
mechanical ventilative means. Cooling load demands on the mechanical plant are
diminished with this strategy.”

2.6. Integrating HVAC system with the façade
(Stec and Paassen 2003) categorized HVAC systems that can be utilized in the cavity in
three general types:
2.6.1. Full HVAC system for the building:
“Where the cavity is not a part of the HVAC system. It may have high results in
energy consumption. However, users can use either the mechanical system or
natural ventilation from the outside”.
2.6.2. Limited HVAC system:
“The cavity has a fully or partial role in influencing the indoor climate. It can
contribute through pre-heating the ventilation air, or extracting warm air in
cooling periods”.
50

2.6.3. No HVAC:
“The double skin façade system can replace the HVAC system. And this can be
fulfilled in temperate or cold climates, leading to low energy consumption”.
(H. Poirazis 2004) described a way to use the cavity as an exhaust duct (Figure 16). The
author claimed that the hot air in multistory high type during the summer can be extracted
through openings at the top of the façade, but this type would not be ideal during the
summer. However, the cavity can be utilized as a duct as a part of the HVAC system
(Figure 17).

Figure 16 Double Skin Façade as an exhaust duct. (H. Poirazis 2004)

51

Figure 17 Double Skin Façade as a duct for the ventilation (H. Poirazis 2004)
(Li 2001) described the mechanical ventilation in the cavity that uses either under floor or
plenum systems to exhaust the air into the cavity mechanically. The exhaust air rises in
the cavity removing the heat and then to be extracted out of the cavity. (Barreneche,
1995)
2.7. The influence of using different glazing types:
(H. Poirazis 2004) stated that double skin facades used common pane types: tempered
single pane for the external skin and double or triple pane with thermal insulation for the
internal skin.
A study by (Hamza 2007) on office buildings in Cairo, Egypt to compare the influence of
glazing properties on the performance of double skin façade was conducted. Three
different glass types were tested on the external skin: clear, tinted, and reflective glazing.
52

Based on the simulation results, the author concluded that: clear glazing on the external
skin is predicted to contribute to increase cooling loads when compared over a single skin
façade using reflective glazing. Moreover, considering lower shading co-efficient and g-
value than transparent (clear) glass on the external skin would provide more protecting
against the intense direct solar radiation in hot arid climates.

2.8. The influence of integrating shading devices:
Metallic or tempered glass louvers can be integrated in the system to provide protection
from direct sun and heat gain. Shading devices can be located inside the cavity or on the
exterior surface.
A paper published in Building and Environment Journal vol. 44 by (Baldinelli 2008) had
analyzed a solution of double skin façade equipped with an integrated movable shading
system in a warm climate area. The paper investigated the system performance on an
office building in central Italy and compared it with opaque wall and glazed wall. As a
result, the author concluded that the proposed façade with integrated shading devices
showed significant improvements on the building energy behavior in the entire year.
(Oesterle 2001) mentioned that an adequately ventilated sun- shading system in the
intermediate space of the double skin façade can have almost the same effect as an
external insulation; and it will be much more efficient than internal sun shading behind
solar-control glass.
53

Shading devices inside the cavity can reradiate the absorbed solar radiation inside the
intermediate space and causes a difference in temperature which results to a stack effect,
hence, rising the air up and exhausting additional heat. (Compagno 2002)

2.9. Case studies:
2.9.1. Sowwah Square, Abu Dhabi, United Arab Emirates:
Goettsch Partners has designed a 529,360 m
2
development with
climate response strategies for the envelope. The building uses a
double skin façade system with mechanically ventilated cavity to
form a buffer zone to provide protection from the harsh external
environment in Abu-Dhabi.

Figure 18 Sowwah Square buildings,
54

At Sowwah Square (Figure 18) the double skin façade type is a
multi-story starting from the fourth floor to the top of the building.
An active solar shading system is integrated on the exterior surface
of the cavity and can track the sun to optimize the shading.
The shading system helped to prevent the intermediate space from
overheating because it has minimized the projected solar energy on
the intermediate space. “Utilizing an outboard lite with a very high
shading coefficient, the design team was able to effectively block
76 percent of the solar energy from ever entering the air cavity.”
(Soberg 2008)
Taking the exhaust air from office spaces and injecting it back to
the cavity to flush out the warm air was used to achieve getting the
intermediate buffer zone (Figure 19).
55

Figure 19 double skin facade system in Sowwah project
Source: http://www.gpchicago.com/users/news_view.asp?FolderID=1829&NewsID=73
According to (Soberg 2008) “Through these efforts, the design
team expects the double-skin cavity to be an average temperature
of 89º F (31 ºC) when the exterior temperature reaches 115º F (46
ºC). This will allow the high U-value of the insulated inner glazing
to more easily block the air cavity’s radiating energy.”

2.9.2. Supreme Audit Court, Tehran, Iran:
A study was conducted by (Hashemi, Fayaz and Sarshar 2010) on
the 12 stories Supreme Audit Court building in Tehran, Iran, which
has a double skin façade on four sides (Figure 20) , by using on-
56

site measurement for 2 weeks in summer and winter to investigate
the behavior of the double skin façade in hot and cold conditions,
in addition to computer simulation studies to observe the building
performance with and without the double skin façade. As a result
of the study, the surface temperature differences between the outer
skin, the inner skin and the air inside cavity can reduce required
heating energy in winter. Cooling loads in summer can be
decreased by applying additional techniques such as night
ventilation and utilizing shading devices

Figure 20 On the left: Supreme Audit Court. On the right: a cross section of the building
2.9.3. Capital Gate, Abu Dhabi, United Arab Emirates:
The 35 stories height building (Figure 21) located in the Capital
Centre development in Abu Dhabi, UAE contains hotel rooms and
various exclusive offices. According to (Schofield 2012) the upper
half of the tower, where hotel levels are, has a double skin façade
to reduce the solar heat gain in the hotel room. The cavity is
57

mechanically ventilated using interior air from the hotel rooms into
the façade and recycles it back to the system to be re-used creating
an insulating buffer zone between the hot outside air and the cool
inside air (Figure 22).

Figure 21 On the right: the Capital Gate Tower. On the left: close up picture showing the two skins
on the upper part of the tower.

Figure 22 the double-skin facade system in the Capital Gate Tower (Schofield 2012)
58

Figure 23 an interior shot of the double skin facade for the upper floors of the tower
2.9.4. Cleveland Clinics, Abu Dhabi, United Arab Emirates:
Cleveland Clinics design by HDR Architecture is one of the distinguished
healthcare projects in Abu Dhabi city in UAE. According to (Jordana 2012), the
double skin façade creates a stack effect allowing the building to breathe. By
placing the mechanical floor at the bottom of the hospital tower, exhausting cool
air that was used within the hospital spaces from the bottom of the tower to the
cavity and eventually extracted out through the roof. This process creates buffer
zone between the hot outside air and the cool interior of the building.
59

Figure 24 On the right: Cleveland Clinic, Abu Dhabi, UAE (Jordana 2012). On the left: Cleveland
Clinic’ double skin façade configuration (Fortmeyer 2009)

2.9.5. Arcapita Bank Headquarters, Manama, Bahrain:
This 10 story office building has been designed by SOM and
evaluated by the T.C. Chan Center (Figure 25). According to the
constructor’s web site (nassgroup.com n.d.), the primary façade
system comprised a double skin façade system that will act as the
building's buffer zone. The cavity is internally mechanically
ventilated with integrated automated sun shading device.
The T.C. Chan Center has simulated and analyzed the cavity
performance (Figure 26). The results showed the performance and
the behavior of the cavity by studying the air movement, flux, and
60

air and surface temperature levels to evaluate its ability to meet the
target criteria. (T.C Chan Center n.d.). The results were requested
for the purposes of re-evaluating in this thesis, but the results were
not made available.

Figure 25 Arcapita Bank HQ

Figure 26 CFD studies for the cavity of Aracbita Bank double skin façade. (T.C Chan Center n.d.)
61

3. Chapter Three: Methodologies

To find the optimized configurations for double skin facades in hot arid climates, a
dynamic thermal simulation analysis is used to investigate the double skin façade
performance and its components behavior. The study has tested several effective
variables on a hypothetical office building model in Riyadh city. The research aims to
compare the energy consumption and thermal performance of a baseline single skin
façade case with and without shading, and multiple configurations of double skin facades
on the same building.
3.1. Data acquisition steps:
To achieve the targeted results, a simulation experiment proceeded in the following
workflow (Figure 27):
3.1.1. Modeling a hypothetical building:
In the first phases of the research, a model was created to test some variables to
understand the software and its modules. After this initial learning process, the model
was refined to get more accurate results.
3.1.2. Test several variables (Preliminary studies):
Based on the background research, a list of different DSF parameters has created. Many
of them have a direct effect on the façade, and others had little or no impact. A group of
the variables were terminated in a final list for testing variables.
62

3.1.3. Final variables list:
The final variables list created several scenarios. The results were collected and exported
to excel sheets to be analyzed to draw conclusions.

Figure 27 Methodolgy and workflow
3.2. Thermal dynamic simulation tool:
IES –VE Pro is the selected building performance simulation tool. It’s a whole building
performance assessment software that can integrate different aspects to analyze the
performance. The abilities it has such as: using detailed HVAC systems, modeling the
double skin façade, and generating detailed results, make it the first choice. IES-VE Pro
was used to model the study’s hypothetical model and the double skin in Riyadh city,
with using weather data downloaded from the U.S Department of Energy’s web site. The
building’s construction and system were specifie d to match the typical office buildings in
Riyadh city.
Background
research
Initial
variables
Hypothetical
model
Simulations
Final variable
list
Initial results
Data
collection
Results
Conclusions
63

IES-VE Pro consists of several modules linked to each other; each module has its own
specialization. The modules listed below are the tools used in this study to provide deep
analysis:
ModelIT: To create a building model with the surrounding context, orientation and
modeling the shading.
SunCast: To calculate solar gains based on the location and the sun’s path. It can
calculate the effect of the shading devices.
ApacheLoads: Based on the weather data, the model, and SunCast results, ApcaheLoads
calculates building loads based on the ASHRAE Heat Balance method.
ApacheHVAC: In cases where the building needs more detailed HVAC system instead of
the default one, ApacheHVAC is the tool to design the layout of the mechanical system
and control its components and values based on the loads generated by ApacheLoads.
MacroFlo: To assign openings of the outer skin to simulate natural ventilation and the
stack effect in cases where the cavity is naturally ventilated.

3.3. Selected hypothetical building:
The hypothetical building is intended to resemble the typical size and construction type
of office buildings in Saudi Arabia specifically in Riyadh city. Opaque surfaces are
usually well insulated, however, practices of implementing glazing on the façade are in
64

general insufficient. Glazing is usually installed without proper shading, and window to
wall ratios are unfortunately high.
3.3.1. Building description and layout:
The selected building is a three stories building, with glazing area of 50%
of each façade. Each floor area is 675 m2. The total built area is 1728 m2
excluding the cavity space. The baseline case layout is divided into five
zones, four equal zones for office use, and a central lobby including
services (Figure 28). The cavity location varies based on the tested
scenarios.

Figure 28 Building layout

65

The building envelope is designed considering the Saudi Building Code
(Table 3).
For the targeted location, the building envelope requirements for
commercial and office buildings are represented in the following table:

Table 3 Based on the building envelope requirement for 3611 < HDD/CDD (
o
C) < 3889 from the
Saudi Building Code.
3.4. Preliminary studies:
In the first phases of the research, and based on the case studies shown, the design
guidelines, and the background research, several variables were tested in preliminary
simulations to determine effective façade components to reduce the number of ineffective
variables. The preliminary simulations have tested various scenarios with different
66

parameters including the installation types, four orientation, different cavity depth
distances, glazing types, shading device location.
The initial results which measured the building’s total energy consumption, total
building’s cooling energy, highest temperature in the cavity, temperature for the external
surface and the two internal skins showed that some of these variables are not effective or
might be have undesirable influences on the façade and the comfort of the occupants. The
main goal to run these simulations is to narrow down the scenarios to get more effective
results.
3.5. Final testing variables:
As a result of the preliminary studies, the proposed variables were reduced to investigate
the most effective items. The variables list (Figure 29) was narrowed down to test several
scenarios of double skin façade:
Installation types:
Multi-story type.
Corridor type.
Box-window type.
Orientation:
Four main orientations.
Cavity depth distance:
100 cm.
67

150 cm.
Glazing types:
Internal skin:
Double glazed Low-E (Fixed)
Exterior skin:
Single glazed reflective coating (Fixed)
Shading device:
Located on the external skin (Fixed)
Ventilation:
Naturally ventilated cavity.
Mechanically ventilated cavity.

68

Figure 29 Final varaibles list

3.6. Model settings and simulation process:
Each scenario needs to go through some preparatory steps and settings before processing
the final simulation. Some of the steps are simple settings in model, and others are basic
simulations or calculations. In general the following is a description of the simulation
process:
3.6.1. Modeling:
This step mostly covers creating the building layout and assigning glazing, construction
materials, thermal properties, and internal loads. It includes also the settings of the
operational profiles and modeling the shading and the cavity with different distances.
(Figure 30) shows an example of a modeled scenario for the hypothetical building with a
100 cm shaded cavity on western façade.
Installation
Type
Multi-
story
Box-
window
Corridor
Direction
South
North
West
East
Cavity
Depth
50 cm
100 cm
150 cm
Glazing
type on the
external
skin
Low - E
Reflective
Shading
Device
Location
External
Inside the
cavity
Ventilation
Natural
Mechanical
69

Figure 30 example of a modeled scenario
3.6.2. Shading calculations:
As mentioned before, IES-VE works on integrated modules. SunCast is the module to
calculate the solar shading all the year (Figure 31). The results can be shown on load
calculations and the final simulation.

Figure 31 A result of SunCast simulation to calculate solar shading
3.6.3. Airflow Setting:
One of the tested variables is ventilation in the cavity, whether it is naturally or
mechanically ventilated. To allow the software to utilize natural ventilation in the cavity,
70

IES-VE uses a MacroFlo module to set the openings. For the external skin, a strip of
openings on the bottom and the top of the skin assigned to be opened to allow the air to
flow inside the cavity and exhaust (Figure 32). The rest of the external skin and other
glazing assigned to be closed (Figure 33)

Figure 32 Assigning the openings in Macroflo

71

Figure 33 Closed openings
This setting would be only effective if the MacroFlo is linked with the final simulation,
otherwise, in cases of mechanically ventilated cavity, it will not be linked.
The following chart (Figure 34) is a result that shows the volume flow in the cavity in
one of the scenarios for a specific day to verify the entrance of the outside air in the
intermediate space:
72

Figure 34 Volume flow in the cavity
3.6.4. HVAC Layout:
IES-VE can use default systems, however, because the need to design a special HVAC
layout for the mechanically ventilated cavity, and the need to get comparable results,
ApacheHVAC module used to design general HVAC layouts for the single skin building,
naturally ventilated cavity and mechanically ventilated cavity scenarios.
The chosen system is a VAV single duct system. In the scenarios where the cavity is
naturally ventilated are tested, there is no need to engage the cavity space in the system
(Figure 35). However, in the mechanically ventilated cavity scenarios, the cavity space is
located after the return fan and before the air outlet (Figure 36). The reason for that is to
inject conditioned exhaust air in the cavity before extracting it out of the building.
00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 00:00
110000
100000
90000
80000
70000
60000
50000
40000
30000
20000
10000
0
Volume flow (l/s)
D ate: Fri 06/Aug
MacroFlo external vent: Cavity (021-m-e-150-rc-ex-n2.aps )
73

Figure 35 Single skin façade and double skin façade (Naturally ventilated cavity) HVAC layouts

Figure 36 Double skin façade (mechanically ventilated cavity) HVAC layout
74

3.6.5. Load calculations:
The last step before the final simulation, total load calculation is needed to be added to
the defined internal loads (people, lighting and equipment). In this step, ASHRAE load
calculation method is going to sum up the total load for each zone and for the total
building load based on the internal loads for each zone and the solar gain calculation
based on the defined construction type, orientation and calculated shading (SunCast
calculations). The first step is to run “zone-level sizing”, which calculates each zone
loads and generates a room sensible cooling and airflow rates report (Figure 37).

Figure 37 An example of a summary report of building heating and cooling performance

75

The resulted airflow for each zone is going to be assigned in the controller for each zone
in the HVAC layout manually for each scenario (Figure 38).

Figure 38 Assigning flow rate for each zone based on the generated report

At the end, system equipment and plant sizing is going to be calculated to obtain the total
system capacity and the fan total airflow.

76

3.6.6. Final simulation:
For each scenario, the final simulation needs to be inked to the correct modules to
calculate the defined variables. SunCast will be always linked. MacroFlo is only linked
when natural ventilation in the cavity is utilized. ApacheHVAC needs to be linked to the
correct system whether the cavity is mechanically ventilated or not. (Figure 39)

Figure 39 Example of the simulation window

77

3.7. Model inputs:
3.7.1. Building construction:
3.7.1.1. Envelope construction and U-values:
Elements Materials Thickness U-Value (W/m
2
K)
Walls Insulated concrete 45.5 cm 0.25
Roof Insulated reinforced- concrete 42.5 cm 0.23
Floors Reinforced- concrete ceilings 30 cm 2.4
Internal walls Concrete blocks 13 cm 1.16
Table 4 Construction materials inputs
3.7.1.2. Glazing properties:
Location Description U-Value
(W/m
2
K)
Total R-Value
(m
2
K/W)
Single skin facades Double glazed windows –
reflective coating
2.92 0.17
Double skin facades:
(External skin)
Single glazed windows –
reflective coating
5.41 0.0057
Double skin facades:
(Internal skin)
Double glazed Low-E
windows
1.67 0.33
Table 5 Glazing inputs
78

3.7.2. Construction of double skin façade:
3.7.2.1. Multi-story type:
This type extends over the three stories without dividers, allowing the air to circulate
from the bottom to the top. The external surfaces are fully glazed, while the interior skin
is 50% glazed and 50% opaque. There are openings in the top and the bottom of the
space. The distance varies depends on the tested cavity distance whether it’s a 100cm or
150cm. Shading devices installed on the external skin (Figure 40).

Figure 40 Multi-story type
79

3.7.2.2. Corridor Type:
This type’s cavity is divided and sealed at each floor level. It has separate openings
unlike the other floor units. It is also fully glazed with floor metal dividers (Figure 41).

Figure 41 Corridor Type
3.7.2.3. Box-window type:
In each floor level, a group of separated sealed cavities with its independent openings
represent the box-window type (Figure 42).
80

Figure 42 Box-window type

3.7.3. Weather data:

Figure 43 Riyadh's weather data
81

The weather data used in the simulations (Figure 43) is acquired from the U.S.
Department of Energy website. It shows that the monthly average mean temperatures
starting from April through October are higher than the comfort zone.

Figure 44 Acquired data from the U.S. Department of Energy including monthly dry bulb
temperatures and solar radiarion.

82

3.7.4. Shading settings:
In the preliminary studies, two locations were examined the performance of shading
device in the double skin facade, outside and inside the cavity. However, the initial
results showed that louvers inside the cavity can absorb and re-radiate the intense solar
radiation. Shading devices were modeled in the final simulations to be on the exterior
skin. To model it in the software, small spaces were created and specified as a “local
shade”.

3.7.5. Spaces thermal conditions and loads:
A space thermal condition is (Figure 45) going to specify the internal load for each zone
and occupational profiles. Those inputs would be included to calculate the loads in the
final simulation.

Figure 45 Thermal conditions settings window
83

3.7.5.1. Office spaces:
The cooling and heating occupational profiles can be set in the Apache HVAC, however,
the systems profiles start from 8:00 am to 6:00 pm with no lunch break five days per
week. Internal loads would include: computers, lighting and people.
3.7.5.2. Circulation:
This is the central lobby of each floor. The occupational profile would be the same as the
office spaces. Internal loads will include lighting, and people.
3.7.5.3. The cavity:
The cavity doesn’t have any internal loads. However, in cases where the exhaust air
injected in the cavity, the occupational profile would follow the building profile.

People occupant
density (m
2
/person)
Lighting sensible
gain (W/m
2
)
Computer sensible
gain (W/m
2
)
Office spaces 14 12 12
Circulation 30 10 0
Cavity 0 0 0
Table 6 Zones’ internal gains summary
3.7.6. Occupation profile:
Commercial and government office building varies in their occupational profiles. The
chosen profile (Figure 46) would resemble commercial offices more. ASHRAE 8:00 am
84

to 6:00 pm No lunch is the main occupational profile for all the building systems. The
profile covers five days per week with no holidays.

Figure 46 Daily occupation profile

3.7.7. HVAC system layout and ventilation settings:
HVAC system for the single skin façade:

Figure 47 HVAC system for the single skin façade and the naturally ventilated cavity
85

Figure 48 System layout for mechanically ventilated multi-story type cavity

Figure 49 System layout for mechanically ventilated corridor type cavity

Figure 50 System layout for mechanically ventilated box-window type cavity

86

3.8. Expected results:
Mainly the results are covering two major aspects; the energy and thermal performance
of the building in baseline cases and double skin façade scenarios (Figure 51). Reducing
the energy consumption is a goal but it must be accomplished without compromising the
comfort of the occupants.

Figure 51 The main three examined scenarios
3.8.1. Energy performance:
Total annual building energy consumption (MWh)
Energy use Intensity ( kW/m
2
)
Total building cooling energy (MWh)
Cooling energy (kW/m
2
)
Room adjacent to the cavity sensible cooling loads in peak day (kW)
Solar gain in rooms adjacent to the cavity in peak day (kW)
87

3.8.2. Thermal performance:
Air temperature in the cavity in peak day (
o
C)
Surface temperature:
Outer skin surface temperature in peak day (
o
C)
Inner glass surface temperature in peak day (
o
C)
Inner concrete surface temperature in peak day (
o
C)
Predicted percentage of dissatisfied occupants in peak day (PPD %)

88

4. Chapter Four: Preliminary Studies

The main reason to conduct preliminary studies is to test the software and to obtain the
advantage of early results to help decide what variables might be the most important to
investigate.
In this phase, the workflow of creating the model, simulating the thermal conditions and
energy consumption, and data gathering has been improved to increase the accuracy of
the data.
4.1. Preliminary testing variables:
Several scenarios of different variables based on common configurations of double skin
facades were simulated. The results showed that some of the variable have no effect or
may have undesired impact on the energy and thermal performance of the building. The
decisions have been made to eliminate those variables in the final variables list (Figure
52) since this research project is looking for optimized configurations for the double skin
façade.

Figure 52 The variables list (the highlighted are the cancelled variables)
Installation
Type
Multi-story
Box window
Corridor
Direction
South
North
West
East
Cavity Depth
50 cm
100 cm
150 cm
Glazing type
on the
external skin
Low - E
Reflective
Shading
Device
Location
External
Inside the
cavity
Ventilation
Natural
Mechanical
89

4.2. Explanation of the undesired variables:
4.2.1. Cavity depth:
Three distances for the cavity depth were investigated: 50cm, 100cm and 150cm. Results
showed that for most of the cases, narrower cavity depth can cause overheating inside the
cavity, which will raise the temperature in the cavity causing more loads on the rooms
adjacent to the cavity and will increase internal surfaces temperature. The chart (Figure
53) shows the difference in surface temperature for inner skin (glass) for scenarios with
50cm 100, and 150cm cavities depth.
24 22 20 18 16 14 12 10 8 6 4 2
31
30
29
28
27
Peak day hours
Suraface temperature ('C)
50cm cavity
100cm cavity
150cm cavity
Variable
Inner galss temperature for 50cm, 100cm, and 150cm cavities

Figure 53 Inner glass temperature in peak day for three cavities' depths for east facing cavity
Moreover, energy consumption for the building increases a bit in cases where 50cm
cavity depth is used (Figure 54). Using wider depth for the cavity would allow more air
90

to flow into the cavity to extract heat; however, using narrower depth would slow down
the air velocity causing overheating. As a result, the 50cm cavity depth will not be
included in the testing variables.

Figure 54 Energy use intensity (kWh/m2) for different cavity depths for cavity facing east

4.2.2. Glazing type on the external skin:
Low-E glazing and reflective coating glazing were tested on the external skin of the
double skin façade. The scenarios where reflective glazing was used were always lower
in energy consumption and air temperature inside the cavity. Sometimes the differences
are very small. Inner glass temperature in cases where Low-E glazing on the external skin
used was increased, which will affect the comfort and cooling loads (Figure 55). Overall,
single reflective glazing on the external glazing and double low-e glazing on the interior
skin are used in the rest of the simulations to get more optimized results in terms of
208
206.5
205
203.5
204
204.5
205
205.5
206
206.5
207
207.5
208
208.5
50 cm cavity 100cm cavity 150cm cavity
Energy consumption Intensity (kWh/m2)
91

energy performance. However, it might have a significant impact on reducing the amount
of daylight transmission compared to the Low-E glazing on the external skin.

24 22 20 18 16 14 12 10 8 6 4 2
34
33
32
31
30
29
28
27
Peak day hours
Surface temperature (C)
Low-E glazing
Reflective coating glazing
Variable
Inner glazing surface temperature for two glazing types scenarios

Figure 55 Inner glazing surface temperature for two glazing types scenarios on the external skin

4.2.3. Shading device location:
In the preliminary studies, two shading device locations were examined: inside the cavity,
and on the external skin of the double skin façade. In general, the results of the scenarios
where the shading is inside the cavity showed that the cavity space temperature is
increased (Figure 56), because the louvers absorb solar radiation and convect re-radiate it
92

in the cavity. External shadings block more solar radiation from entering the cavity and
have better energy performance and inner skin surface temperature (Figure 57).
However, it is important to mention that applying shadings on the external skin instead of
the inside of the cavity would make the louvers unprotected from the external
environmental factors, be exposed to erosion, and make it harder to be accessible for
maintenance.
24 22 20 18 16 14 12 10 8 6 4 2
46
44
42
40
38
36
34
32
30
Peak day hours
Air temperature (C)
Shading in the cavity
External shading
Variable
Air tempearture inside the cavity for two shading locations scenarios

Figure 56 Cavity’s air temperature in peak day for two shading locations scenarios facing east
93

24 22 20 18 16 14 12 10 8 6 4 2
33
32
31
30
29
28
27
Peak day hours
Surface temperature (C)
Shading in the cavity
External shading
Variable
Inner glass surface temperature for two shading locations scenarios

Figure 57 Inner glass temperature in peak day for two shading locations scenarios facing east

94

5. Chapter Five: Study Results

After narrowing down the proposed parameters to examine effective variables to find
optimized configurations for double skin facades, data was collected from running
simulations for baseline cases and double skin facade scenarios using IES-VE. The
scenarios investigate several variables that cover:
 Double skin façade installation types.
o Multistory type.
o Corridor type.
o Box-window type.
 Orientations.
o South
o North
o East
o West
 Cavity depth.
o 100cm
o 150cm
 Ventilation in the cavity.
o Natural
o Mechanical
95

Since this research project examines energy and thermal behavior of double skin facades,
the data in general shows each scenario’s energy and thermal performance results.
Energy results include total annual energy consumption, energy use intensity, cooling
loads, space condition sensible and solar gain in rooms adjacent to the cavities.
Moreover, thermal results include air temperature inside the cavity, external and internal
surfaces temperature and predicted people dissatisfied percentage in rooms adjacent to
the cavity.
5.1. Simulation models numbering:
Due to the large number of tested models and its variables, a numbering system is needed
to ease referencing the results. Numbering for each model starts with: a series number,
first letter of the installation type, first letter of the orientation, cavity depth, RC which
stands for the glazing type, EX which stands for external shading, and finally first letter
of the ventilation type.
For instance: 006-m-n-100-rc-ex-na stands for multi-story type, cavity on the north side
of the building, with depth of 100cm, reflective coating glazing on the external skin, with
external shading and naturally ventilated cavity.

96

5.2. Total annual building energy consumption (MWh)
Air conditioning systems, lighting and equipment loads are included in each scenario’s
results. Lighting and equipment loads are fixed in all of the results; however, based on
the tested variables and their effect, heating, cooling and fan loads vary. The data show
the total annual energy consumption for each scenario sorted based on the installation
typology.
5.2.1. Baseline scenarios:
The first five tested scenarios are for the baseline model (single skin façade) in addition
to four scenarios for different shading locations.
Scenario
Shading
location
Cavity
depth
Ventilation
in the cavity
Annual
energy
consumption
(MWh)
Energy use
intensity
(kW/m
2
)
001.1 NA
NA NA
385.2 222.9
002 South 380 219.9
003 North 385.6 223.1
004 East 376.6 217.9
005 West 372 215.3
Table 7 Total annual building energy consumption (MWh) and energy use intensity (kW/m
2
) for
baseline cases

Figure 58 Total annual building energy consumption (MWh) for baseline cases

385.2
380.0
385.6
376.6
372.0
330.0
350.0
370.0
390.0
001.1-s-s-na-rc-na-na
baseline model
002-s-s-na-rc-ex-na 003-s-n-na-rc-ex-na 004-s-e-na-rc-ex-na 005-s-w-na-rc-ex-na
97

5.2.2. Multi-story type scenarios:
The results show different values for annual energy consumption for multistory type
scenarios based on tested variables: orientation, cavity depth, and ventilation.
Scenario
Cavity
location
Cavity
depth
Ventilation
in the cavity
Annual
energy
consumption
(MWh)
Energy use
intensity
(kW/m
2
)
006
North
100 cm
Natural 375.6 217.4
007 Mechanical 371.5 215.0
009
150 cm
Natural 376.3 217.8
010 Mechanical 371.5 215.0
012
South
100 cm
Natural 370.7 214.5
013 Mechanical 367.2 212.5
015
150 cm
Natural 370.9 214.6
016 Mechanical 366.8 212.3
018
East
100 cm
Natural 361.7 209.3
019 Mechanical 364.1 210.7
021
150 cm
Natural 366.2 211.9
022 Mechanical 362.1 209.5
024
West
100 cm
Natural 361.9 209.4
025 Mechanical 356.9 206.5
027
150 cm
Natural 366.3 212.0
028 Mechanical 360.4 208.6
Table 8 Total annual building energy consumption (MWh) and energy use intensity (kW/m
2
) for
multi-story type scenarios
98

Figure 59 Total annual building energy consumption (MWh) for for multi-story type scenaios
5.2.3. Corridor type scenarios:
Scenario
Cavity
location
Cavity
depth
Ventilation
in the cavity
Annual
energy
consumption
(MWh)
Energy use
intensity
(kW/m
2
)
030
North
100 cm
Natural 375.3 217.2
031 Mechanical 370.3 214.3
033
150 cm
Natural 375.5 217.3
034 Mechanical 370.2 214.2
036
South
100 cm
Natural 371.1 214.8
037 Mechanical 365.7 211.6
039
150 cm
Natural 370.9 214.6
040 Mechanical 365.6 211.6
042
East
100 cm
Natural 367.8 212.8
043 Mechanical 362.8 210.0
045
150 cm
Natural 367.4 212.6
046 Mechanical 362.1 209.5
048
West
100 cm
Natural 360.6 208.7
049 Mechanical 356.2 206.1
051
150 cm
Natural 360.6 208.7
052 Mechanical 355.5 205.7
Figure 60 Total annual building energy consumption (MWh) and energy use intensity (kW/m
2
) for
corridor type scenarios
375.6
371.5
376.3
371.5
370.7
367.2
370.9
366.8
361.7
364.1
366.2
362.1 361.9
356.9
366.3
360.4
330.0
340.0
350.0
360.0
370.0
380.0
390.0
400.0
99

Figure 61 Total annual building energy consumption (MWh) for corridor type scenarios
5.2.4. Box-window type scenarios:
Scenario
Cavity
location
Cavity
depth
Ventilation
in the cavity
Annual
energy
consumption
(MWh)
Energy use
intensity
(kW/m
2
)
54
North
100 cm
Natural 374.6 216.8
55 Mechanical 370 214.1
57
150 cm
Natural 375.2 217.1
58 Mechanical 359.4 208.0
60
South
100 cm
Natural 370.1 214.2
61 Mechanical 365.3 211.4
63
150 cm
Natural 370.1 214.2
64 Mechanical 364.7 211.1
66
East
100 cm
Natural 364.9 211.2
67 Mechanical 360.7 208.7
69
150 cm
Natural 364.9 211.2
70 Mechanical 359.7 208.2
72
West
100 cm
Natural 360.7 208.7
73 Mechanical 355.2 205.6
75
150 cm
Natural 359.9 208.3
76 Mechanical 354.2 205.0
375.3
370.3
375.5
370.2
371.1
365.7
370.9
365.6
367.8
362.8
367.4
362.1
360.6
356.2
360.6
355.5
330.0
340.0
350.0
360.0
370.0
380.0
390.0
400.0
100

Table 9 Total annual building energy consumption (MWh) and energy use intensity (kW/m
2
) for box-
window type scenarios

Figure 62 Total annual building energy consumption (MWh) for box-window type scenarios

374.6
370.0
375.2
359.4
370.1
365.3
370.1
364.7 364.9
360.7
364.9
359.7
360.7
355.2
359.9
354.2
330.0
340.0
350.0
360.0
370.0
380.0
390.0
400.0
101

80 70 60 50 40 30 20 10 0
390
380
370
360
350
Simulation model
Annual energy consumption (MWh)
Baseline case
Single skin with shading
Multi-story type
Corridor type
Box-window type
Variable

Figure 63 Total annual building energy consumption (MWh) for all scenarios

102

5.3. Cooling energy
Other loads are excluded in the following results. Cooling loads show the actual impact
of double skin façade on the energy consumption. The results are shown for the total
annual cooling loads and cooling loads per area. It should be noted that the data are
sorted based on double skin facade installation typology.
5.3.1. Baseline scenarios:
Scenario
Shading
location
Cavity
depth
Ventilation
in the cavity
Annual
cooling
energy
(MWh)
Cooling
energy
intensity
(kW/m
2
)
001.1 NA
NA NA
153.4 88.8
002 South 150.1 86.9
003 North 153.7 88.9
004 East 148.6 86
005 West 146.2 84.6
Table 10 Building's cooling energy for baseline scenarios

Figure 64 Building's cooling energy/m
2
for baseline scenarios
153.4
150.1
153.7
148.6
146.2
0
20
40
60
80
100
120
140
160
001.1-s-s-na-rc-na-na
baseline model
002-s-s-na-rc-ex-na 003-s-n-na-rc-ex-na 004-s-e-na-rc-ex-na 005-s-w-na-rc-ex-na
103

5.3.2. Multi-story type scenarios:
Scenario
Cavity
location
Cavity
depth
Ventilation
in the cavity
Annual
cooling
energy
(MWh)
Cooling
energy
intensity
(kW/m2)
6
North
100 cm
Natural 148.1 85.7
7 Mechanical 145.6 84.3
9
150 cm
Natural 148.5 85.9
10 Mechanical 145.6 84.3
12
South
100 cm
Natural 144.6 83.7
13 Mechanical 142.5 82.5
15
150 cm
Natural 144.8 83.8
16 Mechanical 142.3 82.3
18
East
100 cm
Natural 140 81.0
19 Mechanical 141.3 81.8
21
150 cm
Natural 142.7 82.6
22 Mechanical 140.2 81.1
24
West
100 cm
Natural 140.5 81.3
25 Mechanical 137.6 79.6
27
150 cm
Natural 142.9 82.7
28 Mechanical 139.4 80.7
Table 11 Building's cooling energy for multi-story types scenarios

Figure 65 Building's cooling energy/m
2
for multi-story type scenarios
85.71
84.26
85.94
84.26 83.68
82.47
83.80
82.35
81.02 81.77 82.58
81.13 81.31
79.63
82.70
80.67
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
104

5.3.3. Corridor type scenarios:
Scenario
Cavity
location
Cavity
depth
Ventilation
in the cavity
Annual
cooling
energy
(MWh)
Cooling
energy
intensity
(kW/m2)
30
North
100 cm
Natural 147.9 85.6
31 Mechanical 144.8 83.8
33
150 cm
Natural 148.1 85.7
34 Mechanical 144.8 83.8
36
South
100 cm
Natural 144.9 83.9
37 Mechanical 141.6 81.9
39
150 cm
Natural 144.8 83.8
40 Mechanical 141.5 81.9
42
East
100 cm
Natural 143.5 83.0
43 Mechanical 140.5 81.3
45
150 cm
Natural 143.3 82.9
46 Mechanical 140.1 81.1
48
West
100 cm
Natural 139.8 80.9
49 Mechanical 137 79.3
51
150 cm
Natural 139.8 80.9
52 Mechanical 136.6 79.1
Table 12 Building's cooling energy for corridor type scenarios

Figure 66 Building's cooling ebergy/m
2
for corridor type scenarios
85.59
83.80
85.71
83.80 83.85
81.94
83.80
81.89
83.04
81.31
82.93
81.08 80.90
79.28
80.90
79.05
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
105

5.3.4. Box-window type scenarios:
Scenario
Cavity
location
Cavity
depth
Ventilation
in the cavity
Annual
cooling
energy
(MWh)
Cooling
energy
intensity
(kW/m2)
54
North
100 cm
Natural 147.5 85.4
55 Mechanical 144.7 83.7
57
150 cm
Natural 147.9 85.6
58 Mechanical 139.6 80.8
60
South
100 cm
Natural 144.3 83.5
61 Mechanical 141.3 81.8
63
150 cm
Natural 144.2 83.4
64 Mechanical 140.9 81.5
66
East
100 cm
Natural 141.9 82.1
67 Mechanical 139.2 80.6
69
150 cm
Natural 141.8 82.1
70 Mechanical 138.7 80.3
72
West
100 cm
Natural 139.8 80.9
73 Mechanical 136.4 78.9
75
150 cm
Natural 139.4 80.7
76 Mechanical 135.8 78.6
Table 13 Building's cooling energy for box-window type scenarios
106

Figure 67 Building's cooling energy/m
2
for box-window scenarios

85.36
83.74
85.59
80.79
83.51
81.77
83.45
81.54 82.12
80.56
82.06
80.27 80.90
78.94
80.67
78.59
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
107

Figure 68 Cooling energy for all of the scenarios
108

5.4. Space conditioning sensible (kW):
This indicator represents the cooling loads on targeted spaces. Based on the tested
scenarios, cavities are located in four main orientations. Space conditioning sensible for
rooms adjacent to the cavities is measured to determine the impact of implementing
double skin façade. The space conditioning sensible is measured in (kW) for each hour in
peak day of the Riyadh city’s which is 6
th
of August. Results are sorted based on the
locations of the tested spaces.
5.4.1. South façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
-16
Peak day hours
Space conditioning sensible (kW)
040-c-s-150-rc-ex-m
060-b-s-100-rc-ex-n
061-b-s-100-rc-ex-m
063-b-s-150-rc-ex-n
064-b-s-150-rc-ex-m
001.1-s-s-na-rc-na-na baseline
002-s-s-na-rc-ex-na
012-m-s-100-rc-ex-n
013-m-s-100-rc-ex-m
015-m-s-150-rc-ex-n
016-m-s-150-rc-ex-m
036-c-s-100-rc-ex-n
037-c-s-100-rc-ex-m
039-c-s-150-rc-ex-n
V ariable
South facing spaces

Figure 69 Space conditioning sensible (kW) for south facing spaces in the peak day (6
th
of August)
Maximum space conditioning sensible value is for the baseline cases 001.1 and 002
during the beginning of the occupational hours at (-11.97) kW. Double skin façade
109

scenarios with naturally ventilated cavity are ranging in the middle. Mechanically
ventilated cavities have the lowest space conditioning sensible values.
110

5.4.2. North façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
-16
Peak day hours
Space conditioning sensible (kW)
034-c-n-150-rc-ex-m
054-b-n-100-rc-ex-n
055-b-n-100-rc-ex-m
057-b-n-150-rc-ex-n
058-b-n-15-rc-ex-m
001.2-s-n-na-rc-na-na baseline
003-s-n-na-rc-ex-na
006-m-n-100-rc-ex-n
007-m-n-100-rc-ex-m
009-m-n-150-rc-ex-n
010-m-n-150-rc-ex-m
030-c-n-100-rc-ex-n
031-c-n-100-rc-ex-m
033-c-n-150-rc-ex-n
V ariable
North facing spaces

Figure 70 Space conditioning sensible (kW) for north facing spaces in the peak day (6th of August)

Maximum space conditioning sensible value is for the baseline cases 003 and 001.2
during the beginning of the occupational hours at (-11.97) kW. Double skin façade
scenarios with naturally ventilated cavity are ranging in the middle. Mechanically
ventilated cavities have the lowest space conditioning sensible values.
111

5.4.3. East façade scenarios:

24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
-16
Peak day hours
Space conditioning sensible (kW)
046-c-e-150-rc-ex-m
066-b-e-100-rc-ex-n
067-b-e-100-rc-ex-m
069-b-e-150-rc-ex-n
070-b-e-150-rc-ex-m
001.3-s-e-na-rc-na-na baseline
004-s-e-na-rc-ex-na
018-m-e-100-rc-ex-n
019-m-e-100-rc-ex-m
021-m-e-150-rc-ex-n
022-m-e-150-rc-ex-m
042-c-e-100-rc-ex-n
043-c-e-100-rc-ex-m
045-c-e-150-rc-ex-n
V ariable
East facing spaces

Figure 71 Space conditioning sensible (kW) for east facing spaces in the peak day (6th of August)
Maximum space conditioning sensible value is for the baseline cases 001.3 during the
beginning of the occupational hours at (-15.62) kW. Followed by baseline case with
shading 004 at (-13.16) kW. Double skin façade scenarios with naturally ventilated cavity
are ranging between (-8) kW to (-12) kW during the day. Mechanically ventilated cavities
have the lowest space conditioning sensible values at (-6.68) kW for scenario 070.
112

5.4.4. West façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
-16
Peak day hours
Space conditioning sensible (kW)
052-c-w-150-rc-ex-m
072-b-w-100-rc-ex-n
073-b-w-100-rc-ex-m
075-b-w-150-rc-ex-n
076-b-w-150-rc-ex-m
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
024-m-w-100-rc-ex-n
025-m-w-100-rc-ex-m
027-m-w-150-rc-ex-n
028-m-w-150-rc-ex-m
048-c-w-100-rc-ex-n
049-c-w-100-rc-ex-m
051-c-w-150-rc-ex-n
V ariable
West facing spaces

Figure 72 Space conditioning sensible (kW) for west facing spaces in the peak day (6th of August)
Maximum space conditioning sensible value is for the baseline cases 001.4 during the
end of the occupational hours at (-13.72) kW. Followed by baseline case with shading
005 at the beginning of the occupational hours (-12.33) kW. Double skin façade scenarios
with naturally ventilated cavity are ranging between (-11.29) kW to (-8) kW during the
day. Mechanically ventilated cavities have the lowest space conditioning sensible values
at (-7.17) kW for scenario 076.
113

5.5. Solar gain:
The data below show the solar gain (kW) in rooms adjacent to the cavity to determine the
effect of double skin façade on solar gain. The data sorted based on the orientations,
measured for each hour for the peak day of Riyadh city which is 6
th
of August.
5.5.1. South façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
2.5
2.0
1.5
1.0
0.5
0.0
Time in peak day
Solar gain (kW)
Baseline
Baseline with shading
Multi story ty pe (100cm cav ity )
Multi story ty pe (150cm cav ity )
C orridor ty pe (100 cm cav ity )
C orridor ty pe (150 cm cav ity )
Window-box ty pe (100 cm cav ity )
Window-box ty pe (150 cm cav ity )
V ariable
Solar gain in the south zone

Figure 73 Solar gain (kW) in south facing spaces in the peak day (6th of August)
Maximum detected peak solar gain in spaces facing south is for the baseline case between
11:00 and 14:00 reached to 2.24 kW. The maximum solar gain for the second baseline
model (with shading) is 1.33 kW. Maximum solar gain for double skin façade scenarios
is 0.68 kW for multistory type with 150cm cavity.
114

5.5.2. North façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Time during peak day (6th of August)
Solar gain (kW)
Baseline
Baseline with shading
Multi story ty pe (100cm cav ity )
Multi story ty pe (150cm cav ity )
C orridor ty pe (100 cm cav ity )
C orridor ty pe (150 cm cav ity )
Window-box ty pe (100 cm cav ity )
Window-box ty pe (150 cm cav ity )
V ariable
Solar gain in the North zone

Figure 74 Solar gain (kW) in north facing spaces in the peak day (6th of August)

Maximum detected peak solar gain in spaces facing north is for the baseline case reached
1.51 kW at the beginning of the occupational hours. The maximum solar gain for the
second baseline model (with shading) is 1.33 kW in the middle of the day. Maximum
solar gain for double skin façade scenarios is 0.68 kW for multistory type with 100cm
cavity.
115

5.5.3. East façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
9
8
7
6
5
4
3
2
1
0
Time in peak day
Solar gain (kW)
Baseline
Baseline with shading
Multi story ty pe (100cm cav ity )
Multi story ty pe (150cm cav ity )
C orridor ty pe (100 cm cav ity )
C orridor ty pe (150 cm cav ity )
Window-box ty pe (100 cm cav ity )
Window-box ty pe (150 cm cav ity )
V ariable
Solar gain in the east zone

Figure 75 Solar gain (kW) in east facing spaces in the peak day (6th of August)

Maximum detected peak solar gain in spaces facing east is for the baseline case reached
8.21 kW at the beginning of the occupational hours. The maximum solar gain for the
second baseline model (with shading) is 3.79 kW in the beginning of the day too.
Maximum solar gain for double skin façade scenarios is 2.09 kW for multistory type with
150cm cavity.
116

5.5.4. West façade:
24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Time in peak day
Solar gain (kW)
Baseline
Baseline with shading
Multi story ty pe (100cm cav ity )
Multi story ty pe (150cm cav ity )
C orridor ty pe (100 cm cav ity )
C orridor ty pe (150 cm cav ity )
Window-box ty pe (100 cm cav ity )
Window-box ty pe (150 cm cav ity )
V ariable
Solar gain in thw west zone

Figure 76 Solar gain (kW) in west facing spaces in the peak day (6th of August)

Maximum detected peak solar gain is for the baseline case is between 14:00 and 17:00
reached to 7.94 kW. The maximum solar gain for the second baseline model (with
shading) is 3.59 kW. Maximum solar gain in Double skin façade scenarios is 2.15 kW for
multistory type with 150cm cavity.

117

5.6. Air temperature in the cavity:
Two types of ventilation in cavities were examined to determine source of ventilation
impact on air temperature of cavities. Baseline cases are excluded because they don’t
have cavities. Data combine all tested installation types and are sorted based on the
orientation of the cavity in the peak day (6
th
of august).
5.6.1. South façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Air temperautre (C)
061-b-s-100-rc-ex-m
063-b-s-150-rc-ex-n
064-b-s-150-rc-ex-m
012-m-s-100-rc-ex-n
013-m-s-100-rc-ex-m
015-m-s-150-rc-ex-n
016-m-s-150-rc-ex-m
036-c-s-100-rc-ex-n
037-c-s-100-rc-ex-m
039-c-s-150-rc-ex-n
040-c-s-150-rc-ex-m
060-b-s-100-rc-ex-n
Variable
Air Temperature in south facing cavities

Figure 77 Air temperature in south facing cavities in the peak day (6th of August)
Maximum detected air temperature for naturally ventilated cavities facing south is for
scenario 039: corridor type with 150cm cavity depth, at (46.26 C
o
). Maximum detected
air temperature for mechanically ventilated cavities during the occupational hours is for
scenario 064: box-window with 150cm cavity depth, at (26.42 C
o
).
118

5.6.2. North façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Air temperature (C)
055-b-n-100-rc-ex-m
057-b-n-150-rc-ex-n
058-b-n-15-rc-ex-m
006-m-n-100-rc-ex-n
007-m-n-100-rc-ex-m
009-m-n-150-rc-ex-n
010-m-n-150-rc-ex-m
030-c-n-100-rc-ex-n
031-c-n-100-rc-ex-m
033-c-n-150-rc-ex-n
034-c-n-150-rc-ex-m
054-b-n-100-rc-ex-n
Variable
Air temperature in north facing cavities

Figure 78 Air temperature in north facing cavities in the peak day (6th of August)
Maximum detected air temperature for naturally ventilated cavities facing north is for
scenario 033: corridor type with 150cm cavity depth, at (46.26 C
o
). Maximum detected
air temperature for mechanically ventilated cavities during the occupational hours is for
scenario 064: box-window with 150cm cavity depth, at (26.42 C
o
).
119

5.6.3. East façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Air temperature (C)
067-b-e-100-rc-ex-m
069-b-e-150-rc-ex-n
070-b-e-150-rc-ex-m
018-m-e-100-rc-ex-n
019-m-e-100-rc-ex-m
021-m-e-150-rc-ex-n
022-m-e-150-rc-ex-m
042-c-e-100-rc-ex-n
043-c-e-100-rc-ex-m
045-c-e-150-rc-ex-n
046-c-e-150-rc-ex-m
066-b-e-100-rc-ex-n
Variable
Air temperature in east facing cavities

Figure 79 Air temperature in east facing cavities the peak day (6th of August)
Maximum detected air temperature for naturally ventilated cavities facing east is for
scenario 045: corridor type with 100cm cavity depth, at (50.9 C
o
). Maximum detected air
temperature for mechanically ventilated cavities during the occupational hours is for
scenario 022: multistory with 150cm cavity depth, at (25.86 C
o
).
120

5.6.4. West façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Air temperature (C)
073-b-w-100-rc-ex-m
075-b-w-150-rc-ex-n
076-b-w-150-rc-ex-m
024-m-w-100-rc-ex-n
025-m-w-100-rc-ex-m
027-m-w-150-rc-ex-n
028-m-w-150-rc-ex-m
048-c-w-100-rc-ex-n
049-c-w-100-rc-ex-m
051-c-w-150-rc-ex-n
052-c-w-150-rc-ex-m
072-b-w-100-rc-ex-n
Variable
Air temperature in west facing cavities

Figure 80 Air temperature in west facing cavities the peak day (6th of August)
Maximum detected air temperature for naturally ventilated cavities facing west is for
scenario 051: corridor type with 150cm cavity depth, at (46.71 C
o
). Maximum detected
air temperature for mechanically ventilated cavities during the occupational hours is for
scenario 028: multistory with 150cm cavity depth, at (26.35 C
o
).

121

5.7. Surface temperature:
Measuring surface temperature is necessary to determine thermal performance of double
skin façade especially its influence on inner surfaces. Outer skin and inner skin including
glass and concrete wall are measured during the peak day of Riyadh city. The data are
sorted based on the orientation of the cavities.
5.7.1. Outer skin surface temperature:
South façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
50
45
40
35
30
25
Peak day hours
Surface temperature (C)
061-b-s-100-rc-ex-m
063-b-s-150-rc-ex-n
064-b-s-150-rc-ex-m
012-m-s-100-rc-ex-n
013-m-s-100-rc-ex-m
015-m-s-150-rc-ex-n
016-m-s-150-rc-ex-m
036-c-s-100-rc-ex-n
037-c-s-100-rc-ex-m
039-c-s-150-rc-ex-n
040-c-s-150-rc-ex-m
060-b-s-100-rc-ex-n
Variable
Outer skin temperature for south facing cavities

Figure 81 Outer skin temperature for south facing cavities in the peak day (6th of August)
Maximum detected surface temperature for naturally ventilated cavities facing south is
for scenario 039: corridor type with 150cm cavity depth, at (50.89 C
o
). Maximum
122

detected surface temperature for mechanically ventilated cavities during the occupational
hours is for scenario 013: multistory with 100cm cavity depth, at (46.86 C
o
).
North façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
50
45
40
35
30
25
Peak day hours
Surface temperature (C)
055-b-n-100-rc-ex-m
057-b-n-150-rc-ex-n
058-b-n-15-rc-ex-m
006-m-n-100-rc-ex-n
007-m-n-100-rc-ex-m
009-m-n-150-rc-ex-n
010-m-n-150-rc-ex-m
030-c-n-100-rc-ex-n
031-c-n-100-rc-ex-m
033-c-n-150-rc-ex-n
034-c-n-150-rc-ex-m
054-b-n-100-rc-ex-n
Variable
Outer skin temperature for north facing cavities

Figure 82 Outer skin temperature for north facing cavities in the peak day (6th of August)
Maximum detected surface temperature for naturally ventilated cavities facing north is
for both scenarios 006: multistory type with 100cm cavity depth, 009: multistory type
with 150cm cavity depth at (50.9 C
o
). Maximum detected surface temperature for
mechanically ventilated cavities during the occupational hours is for scenario 007:
multistory with 100cm cavity depth, at (46.95 C
o
).
123

East façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
50
45
40
35
30
25
Peak day hours
Surface temperature (C)
067-b-e-100-rc-ex-m
069-b-e-150-rc-ex-n
070-b-e-150-rc-ex-m
018-m-e-100-rc-ex-n
019-m-e-100-rc-ex-m
021-m-e-150-rc-ex-n
022-m-e-150-rc-ex-m
042-c-e-100-rc-ex-n
043-c-e-100-rc-ex-m
045-c-e-150-rc-ex-n
046-c-e-150-rc-ex-m
066-b-e-100-rc-ex-n
Variable
Outer skin temperature for east facing cavities

Figure 83 Outer skin temperature for east facing cavities in the peak day (6th of August)
Maximum detected surface temperature for naturally ventilated cavities facing east is for
scenario 021: multistory type with 150cm cavity depth at (51 C
o
). Maximum detected
surface temperature for mechanically ventilated cavities during the occupational hours is
for scenarios 019: multistory with 100cm cavity depth, and 022: multistory with 150cm
cavity depth, at (46.89 C
o
).
124

West façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
50
45
40
35
30
25
Peak day hours
Surface temperature (C)
073-b-w-100-rc-ex-m
075-b-w-150-rc-ex-n
076-b-w-150-rc-ex-m
024-m-w-100-rc-ex-n
025-m-w-100-rc-ex-m
027-m-w-150-rc-ex-n
028-m-w-150-rc-ex-m
048-c-w-100-rc-ex-n
049-c-w-100-rc-ex-m
051-c-w-150-rc-ex-n
052-c-w-150-rc-ex-m
072-b-w-100-rc-ex-n
Variable
Outer skin temperature for west facing cavities

Figure 84 Outer skin temperature for west facing cavities in the peak day (6th of August)
Maximum detected surface temperature for naturally ventilated cavities facing west is for
scenario 051: corridor type with 150cm cavity depth at (50.9
o
C). Maximum detected
surface temperature for mechanically ventilated cavities during the occupational hours is
for scenarios 025: multistory with 100cm cavity depth at (47.27
o
C).
125

5.7.2. Inner glass surface temperature
South façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
40.0
37.5
35.0
32.5
30.0
27.5
25.0
Peak day hours
Surface temperature (C)
040-c-s-150-rc-ex-m
060-b-s-100-rc-ex-n
061-b-s-100-rc-ex-m
063-b-s-150-rc-ex-n
064-b-s-150-rc-ex-m
001-s--na-na-rc-na-na baseline
002-s-s-na-rc-ex-na
012-m-s-100-rc-ex-n
013-m-s-100-rc-ex-m
015-m-s-150-rc-ex-n
016-m-s-150-rc-ex-m
036-c-s-100-rc-ex-n
037-c-s-100-rc-ex-m
039-c-s-150-rc-ex-n
V ariable
Inner skin (Glass) temperature for south facing cavities

Figure 85 Inner skin (glass) temperature for south facing cavities in the peak day (6th of August)
Maximum detected inner glass temperature for baseline cases 001.1 and 002 is at (35.58
o
C). Maximum detected inner glass temperature for naturally ventilated cavities facing
south for scenario 012: multistory type with 100cm cavity depth at (29.89
o
C). Maximum
detected glass temperature for mechanically ventilated cavities during the occupational
hours is for scenarios 013: multistory with 150cm cavity depth at (27.19
o
C).
126

North façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
40.0
37.5
35.0
32.5
30.0
27.5
25.0
Peak day hours
Surface temperature (C)
034-c-n-150-rc-ex-m
054-b-n-100-rc-ex-n
055-b-n-100-rc-ex-m
057-b-n-150-rc-ex-n
058-b-n-15-rc-ex-m
001-s--na-na-rc-na-na baseline
003-s-n-na-rc-ex-na
006-m-n-100-rc-ex-n
007-m-n-100-rc-ex-m
009-m-n-150-rc-ex-n
010-m-n-150-rc-ex-m
030-c-n-100-rc-ex-n
031-c-n-100-rc-ex-m
033-c-n-150-rc-ex-n
V ariable
Inner skin (Glass) surface temperature for north facing cavivites

Figure 86 Inner skin (glass) temperature for north facing cavities in the peak day (6th of August)
Maximum detected inner glass temperature for baseline cases is 001.2 at (34.19
o
C).
Maximum detected inner glass temperature for naturally ventilated cavities facing north
is for scenario 006: multistory type with 100cm cavity depth at (29.89
o
C). Maximum
detected glass temperature for mechanically ventilated cavities during the occupational
hours is for scenarios 007: multistory with 100cm cavity depth at (27.2
o
C).
127

East façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
40.0
37.5
35.0
32.5
30.0
27.5
25.0
Peak day hours
Surface temperature (C)
046-c-e-150-rc-ex-m
066-b-e-100-rc-ex-n
067-b-e-100-rc-ex-m
069-b-e-150-rc-ex-n
070-b-e-150-rc-ex-m
001-s--na-na-rc-na-na baseline
004-s-e-na-rc-ex-na
018-m-e-100-rc-ex-n
019-m-e-100-rc-ex-m
021-m-e-150-rc-ex-n
022-m-e-150-rc-ex-m
042-c-e-100-rc-ex-n
043-c-e-100-rc-ex-m
045-c-e-150-rc-ex-n
V ariable
Inner skin (Glass) surface temperature for east facing cavities

Figure 87 Inner skin (glass) temperature for east facing cavities in the peak day (6
th
of August)
Maximum detected inner glass temperature for baseline case 001.3 is (38.11
o
C).
Maximum detected inner glass temperature for baseline case (with shading) is (35.64
o
C).
Maximum detected inner glass temperature for naturally ventilated cavities facing east is
for scenario 021: multistory type with 150cm cavity depth at (29.97
o
C). Maximum
detected glass temperature for mechanically ventilated cavities during the occupational
hours is for scenarios 019: multistory with 100cm cavity depth at (28.45
o
C).
128

West façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
40.0
37.5
35.0
32.5
30.0
27.5
25.0
Peak day hours
Surface temperature (C)
052-c-w-150-rc-ex-m
072-b-w-100-rc-ex-n
073-b-w-100-rc-ex-m
075-b-w-150-rc-ex-n
076-b-w-150-rc-ex-m
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
024-m-w-100-rc-ex-n
025-m-w-100-rc-ex-m
027-m-w-150-rc-ex-n
028-m-w-150-rc-ex-m
048-c-w-100-rc-ex-n
049-c-w-100-rc-ex-m
051-c-w-150-rc-ex-n
V ariable
Inner skin (Glass) surface temperature for west facing cavities

Figure 88 Inner skin (glass) temperature for west facing cavities in the peak day (6
th
of August)
Maximum detected inner glass temperature for baseline case 001.4 is (39.55
o
C).
Maximum detected inner glass temperature for baseline case 005 (with shading) is (35.87
o
C). Maximum detected inner glass temperature for naturally ventilated cavities facing
west is for scenario 027: multistory type with 150cm cavity depth at (31.34
o
C).
Maximum detected glass temperature for mechanically ventilated cavities during the
occupational hours is for scenarios 028: multistory with 150cm cavity depth at (28.45
o
C).
129

5.7.3. Inner wall surface temperature
South façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
30.0
28.8
27.6
26.4
25.2
24.0
Peak day hours
Surface temperature (C)
040-c-s-150-rc-ex-m
060-b-s-100-rc-ex-n
061-b-s-100-rc-ex-m
063-b-s-150-rc-ex-n
064-b-s-150-rc-ex-m
001-s--na-na-rc-na-na baseline
002-s-s-na-rc-ex-na
012-m-s-100-rc-ex-n
013-m-s-100-rc-ex-m
015-m-s-150-rc-ex-n
016-m-s-150-rc-ex-m
036-c-s-100-rc-ex-n
037-c-s-100-rc-ex-m
039-c-s-150-rc-ex-n
V ariable
Inner skin (Wall) temperature for south facing cavities

Figure 89 Inner skin (wall) temperature for south facing cavities in the peak day (6
th
of August)
Maximum detected inner wall temperature for baseline case 001.1 is (27.17
o
C).
Maximum detected inner wall temperature for baseline case (with shading) 002 is (26.97
o
C). Maximum detected inner wall temperature for naturally ventilated cavities facing
south is for scenario 015: multistory type with 150cm cavity depth at (26.41
o
C).
Maximum detected wall temperature for mechanically ventilated cavities during the
occupational hours is for scenarios 016: multistory with 150cm cavity depth at (25.84
o
C).

130

North façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
30.0
28.8
27.6
26.4
25.2
24.0
Peak day hours
Surface temperature (C)
034-c-n-150-rc-ex-m
054-b-n-100-rc-ex-n
055-b-n-100-rc-ex-m
057-b-n-150-rc-ex-n
058-b-n-15-rc-ex-m
001-s--na-na-rc-na-na baseline
003-s-n-na-rc-ex-na
006-m-n-100-rc-ex-n
007-m-n-100-rc-ex-m
009-m-n-150-rc-ex-n
010-m-n-150-rc-ex-m
030-c-n-100-rc-ex-n
031-c-n-100-rc-ex-m
033-c-n-150-rc-ex-n
V ariable
Inner skin (Wall) surface temperature for north facing cavivites

Figure 90 Inner skin (wall) temperature for north facing cavities in the peak day (6
th
of August)
Maximum detected inner wall temperature for baseline case 001.2 is (27.27
o
C).
Maximum detected inner wall temperature for baseline case (with shading) 003 is (26.97
o
C). Maximum detected inner wall temperature for naturally ventilated cavities facing
north is for scenario 009: multistory type with 150cm cavity depth at (26.42
o
C).
Maximum detected wall temperature for mechanically ventilated cavities during the
occupational hours is for scenarios 010: multistory type with 150cm cavity depth at
(25.85
o
C).

131

East façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
30.0
28.8
27.6
26.4
25.2
24.0
Peak day hours
Surface temperature (C)
046-c-e-150-rc-ex-m
066-b-e-100-rc-ex-n
067-b-e-100-rc-ex-m
069-b-e-150-rc-ex-n
070-b-e-150-rc-ex-m
001-s--na-na-rc-na-na baseline
004-s-e-na-rc-ex-na
018-m-e-100-rc-ex-n
019-m-e-100-rc-ex-m
021-m-e-150-rc-ex-n
022-m-e-150-rc-ex-m
042-c-e-100-rc-ex-n
043-c-e-100-rc-ex-m
045-c-e-150-rc-ex-n
V ariable
Inner skin (Wall) surface temperature for east facing cavities

Figure 91 Inner skin (wall) temperature for east facing cavities in the peak day (6
th
of August)
Maximum detected inner wall temperature for baseline case 001.3 is (28
o
C). Maximum
detected inner wall temperature for baseline case (with shading) 004 is (26.93
o
C).
Maximum detected inner wall temperature for naturally ventilated cavities facing east is
for scenario 021: multistory type with 150cm cavity depth at (26.25
o
C). Maximum
detected wall temperature for mechanically ventilated cavities during the occupational
hours is for scenarios 022: multistory type with 150cm cavity depth at (25.76
o
C).

132

West façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
30.0
28.8
27.6
26.4
25.2
24.0
Peak day hours
Surface temperature (C)
052-c-w-150-rc-ex-m
072-b-w-100-rc-ex-n
073-b-w-100-rc-ex-m
075-b-w-150-rc-ex-n
076-b-w-150-rc-ex-m
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
024-m-w-100-rc-ex-n
025-m-w-100-rc-ex-m
027-m-w-150-rc-ex-n
028-m-w-150-rc-ex-m
048-c-w-100-rc-ex-n
049-c-w-100-rc-ex-m
051-c-w-150-rc-ex-n
V ariable
Inner skin (Wall) surface temperature for west facing cavities

Figure 92 Inner skin (wall) temperature for west facing cavities in the peak day (6
th
of August)

Maximum detected inner wall temperature for baseline case 001.4 is (27.45
o
C).
Maximum detected inner wall temperature for baseline case (with shading) 005 is (26.68
o
C). Maximum detected inner wall temperature for naturally ventilated cavities facing
west is for scenario 024: multistory type with 150cm cavity depth at (26.09
o
C).
Maximum detected wall temperature for mechanically ventilated cavities during the
occupational hours is for scenarios 025: multistory type with 150cm cavity depth at
(25.59
o
C).
133

5.8. Comfort in rooms adjacent to the cavity:
To determine the comfort levels predicted percentage of dissatisfied occupants, (PPD%)
was conducted based on a target of less than 15%. Data show the PPD% for rooms
adjacent to cavities on the peak day (6
th
of August) and sorted based on the orientation of
the cavity. For each orientation, the results include baseline cases, the three installation
types, two cavities distances, and the two ventilation types.
5.8.1. South façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
50
40
30
20
10
Peak day hours
PPD %
039-c-s-150-rc-ex-n
040-c-s-150-rc-ex-m
060-b-s-100-rc-ex-n
061-b-s-100-rc-ex-m
063-b-s-150-rc-ex-n
064-b-s-150-rc-ex-m
PPD 15%
001-s--na-na-rc-na-na baseline
002-s-s-na-rc-ex-na
012-m-s-100-rc-ex-n
013-m-s-100-rc-ex-m
015-m-s-150-rc-ex-n
016-m-s-150-rc-ex-m
036-c-s-100-rc-ex-n
037-c-s-100-rc-ex-m
V ariable
PPD in spaces facing south

Figure 93 predicted percentage of dissatisfied occupants for spaces facing south in the peak day (6
th

of August)
Most of the spaces are below the targeted PPD%. Baseline case 001.1 has the highest
PPD among other scenarios at (15.76%), followed by the baseline case 002 (with
shading) at (15.44%). Highest detected PPD for scenarios with naturally ventilated
134

cavities during the occupational hours is for scenario: 015 multi-story type with 150 cm
cavity depth at (13.41%). Highest detected PPD% for scenarios with mechanically
ventilated cavities during the occupational hours is for scenario: 013 multi-story type
with 100 cm cavity depth at (11.7%).
135

5.8.2. North façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
50
40
30
20
10
Index
Data
033-c-n-150-rc-ex-n
034-c-n-150-rc-ex-m
054-b-n-100-rc-ex-n
055-b-n-100-rc-ex-m
057-b-n-150-rc-ex-n
058-b-n-15-rc-ex-m
PPD 15%
001.2-s-n-na-rc-na-na baseline
003-s-n-na-rc-ex-na
006-m-n-100-rc-ex-n
007-m-n-100-rc-ex-m
009-m-n-150-rc-ex-n
010-m-n-150-rc-ex-m
030-c-n-100-rc-ex-n
031-c-n-100-rc-ex-m
V ariable
PPD in spaces facing north

Figure 94 predicted percentage of dissatisfied occupants for spaces facing north in the peak day (6
th

of August)
Most of the spaces are below the targeted PPD%. Baseline case 003 (with shading) has
the highest PPD among other scenarios at (15.39%), followed by the baseline case 001.2
at (15.25%). Highest detected PPD% for scenarios with naturally ventilated cavities
during the occupational hours is for scenario: 006 multi-story type with 100 cm cavity
depth at (11.43%). Highest detected PPD% for scenarios with mechanically ventilated
cavities during the occupational hours is for scenario: 010 multi-story type with 150 cm
cavity depth at (11.68%).
136

5.8.3. East façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
50
40
30
20
10
Peak day hours
PPD
045-c-e-150-rc-ex-n
046-c-e-150-rc-ex-m
066-b-e-100-rc-ex-n
067-b-e-100-rc-ex-m
069-b-e-150-rc-ex-n
070-b-e-150-rc-ex-m
PPD 15%
001-s--na-na-rc-na-na baseline
004-s-e-na-rc-ex-na
018-m-e-100-rc-ex-n
019-m-e-100-rc-ex-m
021-m-e-150-rc-ex-n
022-m-e-150-rc-ex-m
042-c-e-100-rc-ex-n
043-c-e-100-rc-ex-m
V ariable
PPD in spaces facing east

Figure 95 predicted percentage of dissatisfied occupants for spaces facing east in the peak day (6
th
of
August)
Most of the spaces are below the targeted PPD%. Baseline case 001.3 has the highest
PPD among other scenarios at (21.45%), followed by the baseline case 004 (with
shading) at (17.95%). Highest detected PPD% for scenarios with naturally ventilated
cavities during the occupational hours is for scenario: 021 multi-story type with 150 cm
cavity depth at (14.76%). Highest detected PPD% for scenarios with mechanically
ventilated cavities during the occupational hours is for scenario: 019 multi-story type
with 150 cm cavity depth at (12.92%).
137

5.8.4. West façade scenarios:
24 22 20 18 16 14 12 10 8 6 4 2
50
40
30
20
10
Index
Data
051-c-w-150-rc-ex-n
052-c-w-150-rc-ex-m
072-b-w-100-rc-ex-n
073-b-w-100-rc-ex-m
075-b-w-150-rc-ex-n
076-b-w-150-rc-ex-m
PPD 15%
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
024-m-w-100-rc-ex-n
025-m-w-100-rc-ex-m
027-m-w-150-rc-ex-n
028-m-w-150-rc-ex-m
048-c-w-100-rc-ex-n
049-c-w-100-rc-ex-m
V ariable
PPD in spaces facing west

Figure 96 predicted percentage of dissatisfied occupants for spaces facing west in the peak day (6
th
of
August)
Most of the spaces are below the targeted PPD%. Baseline case 001.4 has the highest
PPD among other scenarios at (17.01%), followed by the baseline case 005 (with
shading) at (15.10%). Highest detected PPD% for scenarios with naturally ventilated
cavities during the occupational hours is for scenario: 024 multi-story type with 100 cm
cavity depth at (12.93%). Highest detected PPD% for scenarios with mechanically
ventilated cavities during the occupational hours is for scenario: 028 multi-story type
with 150 cm cavity depth at (12%).
138

6. Chapter Six: Double Skin Facade Scenarios’ Performance

6.1. Double skin façade installation typology performance:
This section evaluates and analyzes double skin façade installation types’ behavior on
energy consumption and thermal performance. Most of the scenarios’ results have minor
differences; nonetheless, the most effective scenarios with highest values have been
chosen to be analyzed. For each scenario, we are going to look at: results review, a
comparison to the baseline cases, and an analysis for the behavior of the scenario.
6.1.1. Multi-story type:
6.1.1.1. Energy performance:
Among the scenarios of the multi-story type, 025-m-w-100-rc-ex-m showed the most
improved performance in terms of energy consumption. This scenario, which faces west
and has 100cm cavity with mechanically ventilated cavity, has total annual energy
consumption of 356.9 MWh (EUI = 206.5 kWh/m
2
). Cooling energy/m
2
value is (79.6
kW/m
2
). For the western room adjacent to the cavity, total space conditioning sensible in
the peak day (6
th
of August) is (-86.23 kW), and maximum solar gain is (2.06 kW).
In comparison to west facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 7.34% compared the baseline case, and a reduction of
4.06% compared to the baseline case with shading. In rooms facing west, space
conditioning sensible in the peak day was reduced 31.4% compared to the baseline case,
and reduced 24.76% compared to the baseline case with shading (Figure 97). Maximum
139

solar gain in the peak day also reduced 74% compared the baseline case and reduced
42.6% compared to the baseline case with shading (Figure 98)
24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
Peak day hours
Space conditioning sensible (kW)
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na.aps
025-m-w-100-rc-ex-m.aps
V ariable
Space conditioning sensible (kW) for 025-m-w-100-rc-ex-m

Figure 97 Space conditioning sensible (kW) for scenario 025-m-w-100-rc-ex-m and baseline cases in
the peak day (6
th
of August)
140

24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Multi story ty pe (100cm cav ity )
V ariable
Solar gain in peak day for scenario 025-m-w-100-rc-ex-m

Figure 98 Solar gain (kW) for scenario 025-m-w-100-rc-ex-m and baseline cases in the peak day (6th
of August)

Figure 99 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 025-m-w-100-rc-ex-m (right)
This scenario showed improved results due to the configuration of the implemented
double skin façade role and external shading of mitigating solar gain in the western room.
141

As a result of the mechanical ventilation in the cavity, reduced air temperature inside the
cavity and surfaces temperature for the inner skin were contributors to lowering the
cooling loads and increasing thermal performance compared to baseline cases.
6.1.1.2. Thermal performance:
In terms of thermal performance, scenario 013-m-s-100-rc-ex-m, which faces south and
has 100cm cavity depth with mechanically ventilated cavity, has an improved thermal
performance among multi-story type scenarios and baseline cases. In the peak day (6
th
of
August) the maximum air temperature inside the cavity is (37.83
o
C) and the average is
(29.77
o
C). Maximum Surfaces temperature for the inner glass is (28.7
o
C) and for the
inner wall is (24.85
o
C). All multi-story scenarios have thermal comfort levels of 100%
during the occupational hours.
In comparison to the south facing baseline cases, 013-m-s-100-rc-ex-m reduced the
maximum inner glass surface temperature by 19.22% compared to the baseline case, and
19.33% compared the baseline case with shading (Figure 100). Moreover, the thermal
comfort level for occupants in the south facing room has increased from 90% for both
baseline cases to 100%.
142

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal performance for 013-m-s-100-rc-ex-m

Figure 100 Thermal performance for scenario 013-m-s-100-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)
In this case, thermal performance has improved due to several elements: external shading
provided protection against high angle direct sun radiation, which will lower solar gain in
the southern room, compared the baseline cases in addition to the extra glass layer on the
outer skin. Furthermore, injecting exhaust air inside the cavity helped to reduce the air
temperature inside the cavity and inner skin surfaces temperature, thus increasing comfort
levels.

143

6.1.2. Corridor type:
6.1.2.1. Energy performance:
Among the scenarios of the corridor type, 052-c-w-150-rc-ex-m showed the most
improved performance in terms of energy consumption. This scenario, which faces west
and has 150cm cavity with mechanically ventilated cavity, has total annual energy
consumption of 355.5 MWh (EUI = 205.7 kWh/m
2
). Cooling energy/m
2
value is (79.1
kW/m
2
). For the western room which adjacent to the cavity, total space conditioning
sensible in the peak day (6
th
of August) is (-83.22 kW), and maximum solar gain is (1.86
kW).
In comparison to west facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 7.71% compared the baseline case, and a reduction of
4.43% compared to the baseline case with shading. In rooms facing west, space
conditioning sensible in the peak day was reduced 33.6% compared to the baseline case,
and reduced 27.4% compared to the baseline case with shading (Figure 101). Maximum
solar gain in the peak day also reduced 76.57% compared the baseline case and reduced
48.19% compared to the baseline case with shading (Figure 102).
144

24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
Peak day hours
Space conditioning sensible (kW)
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
052-c-w-150-rc-ex-m
V ariable
Space conditioning sensible (kW) for 052-c-w-150-rc-ex-m

Figure 101 Space conditioning sensible (kW) for scenario 052-c-w-150-rc-ex-m and baseline cases in
peak day (6th of August)
145

24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Corridor type (150cm cavity)
Variable
Solar gain in peak day for scenario 052-c-w-150-rc-ex-m

Figure 102 Solar gain (kW) for scenario 052-c-w-150-rc-ex-m and baseline cases in peak day (6th of
August)

Figure 103 Figure 69 Solar gain and space conditioning sensible (in the peak day) comparison
between baseline case (left), baseline case with shading (center), and scenario 052-m-w-150-rc-ex-m
(right)
146

Unlike the multi-story type, corridor type’s cavity is divided and sealed per each floor,
which helped to circulate the air in smaller spaces avoiding the possibility of overheating
the air inside the cavity. Also, cavity horizontal metal dividers provided extra shading
which helped to reduce the solar gain, therefore reducing cooling loads. Injecting exhaust
air inside the cavity reduced air temperature inside the cavity and surfaces temperature
for the inner skin, which also, helped to improve the energy performance.
6.1.2.2. Thermal performance:
In terms of thermal performance, scenario 034-c-n-150-rc-ex-m, which faces north and
has 150cm cavity depth with mechanically ventilated cavity, has an improved thermal
performance among corridor type scenarios and baseline cases. In the peak day (6
th
of
August) the maximum air temperature inside the cavity is (37.27
o
C) and the average is
(29.77
o
C). Maximum Surfaces temperature for the inner glass is (28.67
o
C) and for the
inner wall is (24.74
o
C). All the corridor type scenarios have thermal comfort level of
100% during the occupational hours.
In comparison to the north facing baseline cases, 034-c-n-150-rc-ex-m reduced the
maximum inner glass surface temperature by 16.14% compared to the baseline case, and
19.65% compared the baseline case with shading. Moreover, the thermal comfort level
for occupants in the north facing room has increased from 90% for both baseline cases to
100% (Figure 104).
147

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Paak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal perofrmance of 034-c-n-150-rc-ex-m

Figure 104 Thermal performance for scenario 034-c-n-150-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)
In this case, thermal performance has improved due to several elements: in addition to the
extra shading that the cavity horizontal dividers provide, north facing facades are not
exposed to direct sun during the peak day, which will have lower direct solar gain in the
northern rooms compared the western and the eastern rooms, furthermore, injecting
exhaust air from the mechanical system inside the cavity helped to reduce the air
temperature inside the cavity and surfaces temperature resulting to lower loads the rooms
adjacent to the cavity.
148

6.1.3. Box-window type:
6.1.3.1. Energy performance:
Among the scenarios of the box-window type, 076-b-w-150-rc-ex-m showed the most
improved performance in terms of energy consumption. This scenario, which faces west
and has 150cm cavity with mechanically ventilated cavity, has total annual energy
consumption of 354.2 MWh (EUI = 205 kWh/m
2
). Cooling energy/m
2
value is (78.6
kW/m
2
). For the western room which adjacent to the cavity, total space conditioning
sensible in the peak day (6
th
of August) is (-82.34 kW), and maximum solar gain is (1.78
kW).
In comparison to west facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 8.04% compared the baseline case, and a reduction of
4.78% compared to the baseline case with shading. In rooms facing west, space
conditioning sensible in the peak day was reduced 34.32% compared to the baseline case,
and reduced 28.16% compared to the baseline case with shading (Figure 105). Maximum
solar gain in the peak day also reduced 77.58% compared the baseline case and reduced
50.41% compared to the baseline case with shading (Figure 106).
149

24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
Peak day hours
Space conditioning sensible (kW)
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
076-b-w-150-rc-ex-m
V ariable
Space conditioning sensible (kW) for 076-b-w-150-rc-ex-m

Figure 105 Space conditioning sensible (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in
peak day (6th of August)
150

24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (150cm cav ity )
V ariable
Solar gain in peak day for scenario 076-b-w-150-rc-ex-m

Figure 106 Solar gain (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in peak day (6th of
August)

Figure 107 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 076-b-w-150-rc-ex-m (right)
In addition to the external shading, box-window type’ s cavity has vertical and horizontal
dividers which have a direct impact on reducing solar gain by adding extra shading and
151

minimizing the cavity to smaller spaces to avoid overheating. The combination of the
mentioned elements provides reduction in energy consumption compared to baseline
cases. Injecting exhaust air inside the cavity reduced air temperature inside the cavity and
surfaces temperature for the inner skin, which also, helped to improve the energy
performance.
6.1.3.2. Thermal performance:
In terms of thermal performance, scenario 058-b-n-150-rc-ex-m, which faces north and
has 150cm cavity depth with mechanically ventilated cavity, has an improved thermal
performance among box-window type scenarios and baseline cases. In the peak day (6
th

of August) the maximum air temperature inside the cavity is (37.15
o
C) and the average is
(29.57
o
C). Maximum Surfaces temperature for the glass (Inner skin) is (28.36
o
C) and
for the wall is (24.56
o
C). All the box-window type scenarios have thermal comfort level
of 100% during the occupational hours.
In comparison to the north facing baseline cases, 058-b-n-150-rc-ex-m reduced the
maximum glass surface temperature by 17.05% compared to the baseline case, and
20.27% compared the baseline case with shading. Moreover, the thermal comfort level
for occupants in the north facing room has increased from 90% for both baseline cases to
100% (Figure 108).
152

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal perofrmance of scenario 058-b-n-15-rc-ex-m

Figure 108 Thermal performance for scenario 058-b-n-150-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)
In this case, thermal performance has improved due to several elements; in addition to the
extra shading that the box-window cavity’s dividers provide, north facing facades are not
exposed to direct sun during the peak day, which will have lower solar gain in the
northern rooms compared the western and the eastern rooms, Furthermore, injecting
exhaust air inside the cavity helped to reduce the air temperature inside the cavity and
surfaces temperature resulting to lower loads the rooms adjacent to the cavity.

153

6.2. Double skin façade behavior in different orientations:
This section evaluates and analyzes double skin façade behavior in different orientation
and their influence on energy consumption and thermal performance. Most of the
scenarios’ results have minor differences; however, the most effective scenarios with
highest values have been chosen to be analyzed. For each scenario, we are going to look
at: results review, a comparison to the baseline cases, and an analysis for the behavior of
the scenario.
6.2.1. South façade
6.2.1.1. Energy performance:
South facing scenarios with different configurations are ranging between 371.1 – 364.7
MWh (214.8 – 211.1 kW/m
2
). 064-b-s-150-rc-ex-m showed the most improved
performance in terms of energy consumption. This scenario, which faces south and has
150cm cavity with mechanically ventilated cavity, has total annual energy consumption
of 364.7 MWh (EUI = 211 kWh/m
2
). Cooling energy/m
2
value is (81.5 kW/m
2
). For the
southern room which adjacent to the cavity, total space conditioning sensible in the peak
day (6
th
of August) is (-80.22 kW), and maximum solar gain is (0.39 kW).
In comparison to south facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 5.32% compared the baseline case, and a reduction of
4.02% compared to the baseline case with shading. In rooms facing south, space
conditioning sensible in the peak day was reduced 27.56% compared to the both baseline
cases (Figure 109). Maximum solar gain in the peak day also reduced 82.6% compared
154

the baseline case and reduced 70.67% compared to the baseline case with shading (Figure
110).
24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
Peak day hours
Space conditioning sensible (kW)
001-s--na-na-rc-na-na baseline
002-s-s-na-rc-ex-na
064-b-s-150-rc-ex-m
V ariable
Space conditioning sensible (kW) for 064-b-s-150-rc-ex-m

Figure 109 Space conditioning sensible (kW) for scenario 064-b-s-150-rc-ex-m and baseline cases in
peak day (6th of August)

155

24 22 20 18 16 14 12 10 8 6 4 2
2.5
2.0
1.5
1.0
0.5
0.0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (150cm cav ity )
V ariable
Solar gain in peak day for scenario 064-b-s-150-rc-ex-m

Figure 110 Solar gain (kW) for scenario 064-b-s-150-rc-ex-m and baseline cases in peak day (6th of
August)

Figure 111 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 064-b-s-150-rc-ex-m (right)
156

064-b-s-150-rc-ex-m showed the best energy performance among south facing scenarios
with different configurations. The extra shading provided by box-window type’ s cavity
has a significant impact in reducing solar gain and minimizing the cavity volume to avoid
overheating. The combinations of the mentioned elements provided reduction in energy
consumption compared to baseline cases. Injecting exhaust air inside the cavity reduced
air temperature inside the cavity and surfaces temperature for the inner skin, which also
helped to reduce the cooling loads and improve the energy performance.
6.2.1.2 Thermal performance:
South facing scenarios’ inner glass maximum surface temperature in peak day are
ranging between 29.91
o
C – 28.42
o
C . Scenario 061-b-n-100-rc-ex-m, which faces south
and has 100cm cavity depth with mechanically ventilated cavity, has an improved
thermal performance among south facing scenarios and baseline cases. In the peak day
(6
th
of August) the maximum air temperature inside the cavity is (37.16
o
C) and the
average is (29.72
o
C). Maximum Surfaces temperature for the glass (Inner skin) is (28.42
o
C) and for the wall is (24.67
o
C). All the south facing scenarios have a thermal comfort
level of 100% during the occupational hours.
In comparison to the south facing baseline cases, 061-b-n-100-rc-ex-m reduced the
maximum glass surface temperature by 20% compared to the baseline case, and 20.12%
compared the baseline case with shading (Figure 112). Moreover, the thermal comfort
level for occupants in the north facing room has increased from 90% for both baseline
cases to 100%.
157

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal performance of scenario 061-b-s-100-rc-ex-m

Figure 112 Thermal performance for scenario 061-b-s-100-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)

In this case, thermal performance has improved due to several elements; extra shading
that the box-window cavity’s dividers provide d helped to avoid high angle summer sun,
causing lower solar gain in the southern rooms compared to the western and the eastern
rooms, Furthermore, injecting exhaust air inside the cavity helped to reduce the air
temperature inside the cavity and surfaces temperature.

158

6.2.2. North façade
6.2.2.1. Energy performance:
North facing scenarios with different configurations are ranging between 376.3 – 359.4
MWh (217.8 – 208 kW/m
2
). 058-b-n-150-rc-ex-m showed the most improved
performance in terms of energy consumption. This scenario, which faces north and has
150cm cavity with mechanically ventilated cavity, has total annual energy consumption
of 359.4 MWh (EUI = 208 kWh/m
2
). Cooling energy/m
2
value is (80.8 kW/m
2
). For the
northern room which adjacent to the cavity, total space conditioning sensible in the peak
day (6
th
of August) is (-81.77 kW), and maximum solar gain is (0.39 kW).
In comparison to north facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 6.7% compared the baseline case, and a reduction of
6.8% compared to the baseline case with shading. In rooms facing north, space
conditioning sensible in the peak day was reduced 25% compared to the baseline case,
and 26.34% to the baseline case with shading (Figure 113). Maximum solar gain in the
peak day also reduced 74.34% compared the baseline case and reduced 70.67% compared
to the baseline case with shading (Figure 114).
159

24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
Peak day hours
Space conditioning sensible (kW)
001-s--n-na-rc-na-na baseline
003-s-n-na-rc-ex-na
058-b-n-150-rc-ex-m
Variable
Space conditioning sensible (kW) for 058-b-n-150-rc-ex-m

Figure 113 Space conditioning sensible (kW) for scenario 058-b-n-150-rc-ex-m and baseline cases in
peak day (6th of August)

160

24 22 20 18 16 14 12 10 8 6 4 2
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (150 cm cav ity )
V ariable
Solar gain in peak day for scenario 058-b-n-150-rc-ex-m

Figure 114 Solar gain (kW) for scenario 058-b-n-150-rc-ex-m and baseline cases in the peak day (6th
of August)

Figure 115 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 058-b-n-150-rc-ex-m (right)
161

058-b-n-150-rc-ex-m showed the best energy performance among north facing scenarios
with different configurations. Extra shading provided by box-window type’ cavity has a
significant impact in reducing solar gain and minimizing the cavity volume to avoid
overheating. The combinations of the mentioned elements provided reduction in energy
consumption compared to baseline cases. Injecting exhaust air inside the cavity reduced
air temperature inside the cavity and surfaces temperature for the inner skin, which also,
helped to reduce the cooling loads and improve the energy performance.
6.2.2.2. Thermal performance:
North facing scenarios’ inner glass maximum surface temperature in peak day are
ranging between 29.89
o
C – 28.36
o
C . Scenario 058-b-n-150-rc-ex-m, which faces north
and has 150cm cavity depth with mechanically ventilated cavity, has an improved
thermal performance among north facing scenarios and baseline cases. In the peak day
(6
th
of August) the maximum air temperature inside the cavity is (37.15
o
C) and the
average is (29.57
o
C). Maximum Surfaces temperature for the glass (Inner skin) is (28.36
o
C) and for the wall is (24.56
o
C). All the north facing scenarios have thermal comfort
level of 100% during the occupational hours.
In comparison to the north facing baseline cases, 058-b-n-150-rc-ex-m reduced the
maximum glass surface temperature by 17.05% compared to the baseline case, and
20.26% compared the baseline case with shading (Figure 116). Moreover, the thermal
comfort level for occupants in the north facing room has increased from 90% for both
baseline cases to 100%.
162

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal perofrmance of scenario 058-b-n-150-rc-ex-m

Figure 116 Thermal performance for scenario 058-b-n-150-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)
In this case, thermal performance has improved due to several elements; extra shading
that the box-window cavity’s dividers in addition to injecting exhaust air inside the cavity
helped to reduce the air temperature inside the cavity and surfaces temperature. Providing
more comfort levels compared with baseline cases.

163

6.2.3. East façade
6.2.3.1. Energy performance:
East facing scenarios with different configurations are ranging between 367.8 – 359.7
MWh (212.8 – 208.2 kW/m
2
). 070-b-e-150-rc-ex-m showed the most improved
performance in terms of energy consumption. This scenario, which faces east and has
150cm cavity with mechanically ventilated cavity, has total annual energy consumption
of 359.7 MWh (EUI = 208.2 kWh/m
2
). Cooling energy/m
2
value is (80.3 kW/m
2
). For the
eastern room which adjacent to the cavity, total space conditioning sensible in the peak
day (6
th
of August) is (-82.58 kW), and maximum solar gain is (1.66 kW).
In comparison to east facing baseline cases, the mentioned scenario showed a total energy
consumption reduction of 6.62% compared the baseline case, and a reduction of 4.48%
compared to the baseline case with shading. In rooms facing south, space conditioning
sensible in the peak day was reduced 35% compared to the baseline case, and 28.17% to
the baseline case with shading (Figure 117). Maximum solar gain in the peak day also
reduced 79.75% compared the baseline case and reduced 56.20% compared to the
baseline case with shading (Figure 118).
164

24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
-16
Peak day hours
Space conditioning sensible (kW)
001.3-s--e-na-rc-na-na baseline
004-s-e-na-rc-ex-na
070-b-e-150-rc-ex-m
V ariable
Space conditioning sensible (kW) for 070-b-e-150-rc-ex-m

Figure 117 Space conditioning sensible (kW) for scenario 070-b-e-150-rc-ex-m and baseline cases in
peak day (6th of August)

165

24 22 20 18 16 14 12 10 8 6 4 2
9
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (150 cm cav ity )
V ariable
Solar gain in peak day for scenario 070-b-e-150-rc-ex-m

Figure 118 Solar gain (kW) for scenario 070-b-e-150-rc-ex-m and baseline cases in the peak day (6th
of August)

Figure 119 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 070-b-e-150-rc-ex-m (right)
166

070-b-e-150-rc-ex-m showed the best energy performance among east facing scenarios
with different configurations. Extra shading provided by box-window type’ cavity has a
significant impact in reducing solar gain and minimizing the cavity volume to avoid
overheating. The combinations of the mentioned elements provided reduction in energy
consumption compared to baseline cases. Injecting exhaust air inside the cavity reduced
air temperature inside the cavity and surfaces temperature for the inner skin, which also,
helped to reduce the cooling loads and improve the energy performance.
6.2.3.2. Thermal performance:
South facing scenarios’ inner glass maximum surface temperature in peak day are
ranging between 31.46
o
C – 30.74
o
C . Scenario 070-b-e-150-rc-ex-m, which faces east
and has 150cm cavity depth with mechanically ventilated cavity, has an improved
thermal performance among east facing scenarios and baseline cases. In the peak day (6
th

of August) the maximum air temperature inside the cavity is (41.23
o
C) and the average is
(30.07
o
C). Maximum Surfaces temperature for the glass (Inner skin) is (31.09
o
C) and
for the wall is (24.68
o
C). All the east facing scenarios have thermal comfort level of
100% during the occupational hours.
In comparison to the south facing baseline cases, 070-b-e-150-rc-ex-m reduced the
maximum glass surface temperature by 18.5% compared to the baseline case, and
12.76% compared the baseline case with shading (Figure 120). Moreover, the thermal
comfort level for occupants in the north facing room has increased from 60% and 70%
for the baseline cases to 100%.
167

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal perofrmance of scenario 070-b-e-150-rc-ex-m

Figure 120 Thermal performance for scenario 070-b-e-150-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)

In this case, thermal performance has improved due to several elements; extra shading
that the box-window cavity’s dividers provided helped to avoid direct sun light, causing
lower solar gain in the eastern rooms compared to the baseline cases, Furthermore,
injecting exhaust air inside the cavity helped to reduce the air temperature inside the
cavity and surfaces temperature.

168

6.2.4. West façade
6.2.4.1. Energy performance:
West facing scenarios with different configurations are ranging between 366.3 – 354.2
MWh (212 – 205 kW/m
2
). 076-b-w-150-rc-ex-m showed the most improved performance
in terms of energy consumption. This scenario, which faces west and has 150cm cavity
with mechanically ventilated cavity, has total annual energy consumption of 354.2 MWh
(EUI = 205 kWh/m
2
). Cooling energy/m
2
value is (78.6 kW/m
2
). For the western room
which adjacent to the cavity, total space conditioning sensible in the peak day (6
th
of
August) is (-82.34 kW), and maximum solar gain is (1.78 kW).

In comparison to west facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 8.04% compared the baseline case, and a reduction of
4.78% compared to the baseline case with shading. In rooms facing west, space
conditioning sensible in the peak day was reduced 34.32% compared to the baseline case,
and reduced 28.16% compared to the baseline case with shading (Figure 121). Maximum
solar gain in the peak day also reduced 77.58% compared the baseline case and reduced
50.41% compared to the baseline case with shading (Figure 122).
169

24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
Peak day hours
Space conditioning sensible (kW)
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
076-b-w-150-rc-ex-m
V ariable
Space conditioning sensible (kW) for 076-b-w-150-rc-ex-m

Figure 121 Space conditioning sensible (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in
peak day (6th of August)
170

24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (150cm cav ity )
V ariable
Solar gain in peak day for scenario 076-b-w-150-rc-ex-m

Figure 122 Solar gain (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in the peak day (6th
of August)

Figure 123 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 076-b-w-150-rc-ex-m (right)

171

076-b-w-150-rc-ex-m showed the best energy performance among west facing scenarios
with different configurations. Extra shading provided by box-window type’ cavity has a
significant impact in reducing solar gain and minimizing the cavity volume to avoid
overheating. The combinations of the mentioned elements provided reduction in energy
consumption compared to baseline cases. Injecting exhaust air inside the cavity reduced
air temperature inside the cavity and surfaces temperature for the inner skin, which also,
helped to reduce the cooling loads and improve the energy performance.
6.2.4.2. Thermal performance:
West facing scenarios’ inner glass maximum surface temperature in peak day are ranging
between 31.34
o
C – 28.5
o
C . Scenario 076-b-w-150-rc-ex-m, which faces west and has
150cm cavity depth with mechanically ventilated cavity, has an improved thermal
performance among west facing scenarios and baseline cases. In the peak day (6
th
of
August) the maximum air temperature inside the cavity is (37.33
o
C) and the average is
(29.67
o
C). Maximum Surfaces temperature for the glass (Inner skin) is (28.5
o
C) and for
the wall is (24.8
o
C). All the west facing scenarios have thermal comfort level of 100%
during the occupational hours.
In comparison to the west facing baseline cases, 076-b-w-150-rc-ex-m reduced the
maximum glass surface temperature by 28% compared to the baseline case, and 20.5%
compared the baseline case with shading (Figure 124). Moreover, the thermal comfort
level for occupants in the north facing room has increased from 60% and 90% for the
baseline cases to 100%.
172

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal performance for scenario 076-b-w-150-rc-ex-m

Figure 124 Thermal performance for scenario 076-b-w-150-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)

In this case, thermal performance has improved due to several elements; extra shading
that the box-window cavity’s dividers provided helped to avoid direct sun light, causing
lower solar gain in the eastern rooms compared to the baseline cases, Furthermore,
injecting exhaust air inside the cavity helped to reduce the air temperature inside the
cavity and surfaces temperature.

173

6.3. Cavity depth effect:
This section evaluates and analyzes the cavity’s depth influence on energy consumption
and thermal performance. Most of the scenarios’ results have minor differences;
however, the most effective scenarios with highest values have been chosen to be
analyzed. For each scenario, we are going to look at: results review, a comparison to the
baseline cases, and an analysis for the behavior of the scenario.
6.3.1. 100 cm:
6.3.1.1. Energy performance:
Total energy consumption for double skin facades with 100 cm cavity depth scenarios are
ranging between 375.6 – 355.2 MWh (217.4 – 205.6 kW/m
2
). 073-b-w-100-rc-ex-m
showed the most improved performance in terms of energy consumption. This scenario,
which faces west and has 100cm cavity with mechanically ventilated cavity, has total
annual energy consumption of 355.2 MWh (EUI = 205.6 kWh/m
2
). Cooling energy/m
2

value is (78.9 kW/m
2
). For the western room which adjacent to the cavity, total space
conditioning sensible in the peak day (6
th
of August) is (-82.87 kW), and maximum solar
gain is (1.81 kW).

In comparison to west facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 7.78% compared the baseline case, and a reduction of
4.51% compared to the baseline case with shading. In rooms facing west, space
conditioning sensible in the peak day was reduced 33.9 % compared to the baseline case,
174

and reduced 27.7% compared to the baseline case with shading (Figure 125). Maximum
solar gain in the peak day also reduced 77.2 % compared the baseline case and reduced
49.61% compared to the baseline case with shading (Figure 126).
24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
Peak day hours
Space conditioning sensible (kW)
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
073-b-w-100-rc-ex-m
V ariable
Space conditioning sensible (kW) for 073-b-w-100-rc-ex-m

Figure 125 Space conditioning sensible (kW) for scenario 073-b-w-100-rc-ex-m and baseline cases in
peak day (6th of August)

175

24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (100 cm cav ity )
V ariable
Solar gain in peak day for scenario 073-b-w-100-rc-ex-m

Figure 126 Solar gain (kW) for scenario 073-b-w-100-rc-ex-m and baseline cases in the peak day (6th
of August)

Figure 127 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 073-b-w-100-rc-ex-m (right)
176

073-b-w-100-rc-ex-m showed the best energy performance among double skin facade
scenarios with 100cm depth. Extra shading provided by box-window type’ cavity has a
significant impact in reducing solar gain and minimizing the cavity volume to avoid
overheating. The combinations of the mentioned elements provided reduction in energy
consumption compared to baseline cases. Injecting exhaust air inside the cavity reduced
air temperature inside the cavity and surfaces temperature for the inner skin, which also,
helped to reduce the cooling loads and improve the energy performance.
6.3.1.2. Thermal performance:
Inner glass maximum surface temperature for scenarios with 100cm in peak day are
ranging between 31.64
o
C – 28.42
o
C . Scenario 061-b-s-10-rc-ex-m, which faces south
and has 100cm cavity depth with mechanically ventilated cavity, has an improved
thermal performance among 100cm cavity depth scenarios and baseline cases. In the peak
day (6
th
of August) the maximum air temperature inside the cavity is (37.16
o
C) and the
average is (29.72
o
C). Maximum Surfaces temperature for the glass (Inner skin) is (28.42
o
C) and for the wall is (24.67
o
C). All scenarios with 100cm cavity depth have thermal
comfort level of 100% during the occupational hours.
In comparison to the west facing baseline cases, 061-b-s-10-rc-ex-m reduced the
maximum glass surface temperature by 20% compared to the baseline case, and 20.12%
compared the baseline case with shading (Figure 128). Moreover, the thermal comfort
level for occupants in the north facing room has increased from 90% for both baseline
cases to 100%.
177

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal performance of scenario 061-b-s-100-rc-ex-m

Figure 128 Thermal performance for scenario 061-b-s-100-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)
In this case, thermal performance has improved due to several elements; extra shading
that the box-window cavity’s dividers provided helped to avoid high angle summer sun,
causing lower solar gain in the southern rooms compared to the western and the eastern
rooms, Furthermore, injecting exhaust air inside the cavity helped to reduce the air
temperature inside the cavity and surfaces temperature.
178

6.3.2. 150 cm:
6.3.2.1. Energy performance:
Total energy consumption for double skin facades with 150 cm cavity depth scenarios are
ranging between 376.3 – 354.2 MWh (217.8 – 205 kW/m
2
). 076-b-w-150-rc-ex-m
showed the most improved performance in terms of energy consumption. This scenario,
which faces west and has 150cm cavity with mechanically ventilated cavity, has total
annual energy consumption of 354.2 MWh (EUI = 205 kWh/m
2
). Cooling energy/m
2

value is (78.6 kW/m
2
). For the western room which adjacent to the cavity, total space
conditioning sensible in the peak day (6
th
of August) is (-82.34 kW), and maximum solar
gain is (1.78 kW).
In comparison to west facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 8.04% compared the baseline case, and a reduction of
4.78% compared to the baseline case with shading. In rooms facing west, space
conditioning sensible in the peak day was reduced 34.32% compared to the baseline case,
and reduced 28.16% compared to the baseline case with shading (Figure 129). Maximum
solar gain in the peak day also reduced 77.58% compared the baseline case and reduced
50.41% compared to the baseline case with shading (Figure 130).

179

24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
Peak day hours
Space conditioning sensible (kW)
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
076-b-w-150-rc-ex-m
V ariable
Space conditioning sensible (kW) for 076-b-w-150-rc-ex-m

Figure 129 Space conditioning sensible (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in
peak day (6th of August)
180

24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (150cm cav ity )
V ariable
Solar gain in peak day for scenario 076-b-w-150-rc-ex-m

Figure 130 Solar gain (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in the peak day (6th
of August)

Figure 131 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 076-b-w-150-rc-ex-m (right)

181

076-b-w-150-rc-ex-m showed the best energy performance among west facing scenarios
with different configurations. Extra shading provided by box-window type’ cavity has a
significant impact in reducing solar gain and minimizing the cavity volume to avoid
overheating. The combinations of the mentioned elements provided reduction in energy
consumption compared to baseline cases. Injecting exhaust air inside the cavity reduced
air temperature inside the cavity and surfaces temperature for the inner skin, which also,
helped to reduce the cooling loads and improve the energy performance.
6.3.2.2. Thermal performance:
Inner glass maximum surface temperature for scenarios with 150cm in peak day are
ranging between 31.37
o
C – 28.36
o
C . Scenario 058-b-n-150-rc-ex-m, which faces north
and has 150cm cavity depth with mechanically ventilated cavity, has an improved
thermal performance among scenarios with 150cm cavity depth and baseline cases. In the
peak day (6
th
of August) the maximum air temperature inside the cavity is (37.15
o
C) and
the average is (29.57
o
C). Maximum Surfaces temperature for the glass (Inner skin) is
(28.36
o
C) and for the wall is (24.56
o
C). All the scenarios with 150 cm cavity depth have
thermal comfort level of 100% during the occupational hours.
In comparison to the north facing baseline cases, 058-b-n-150-rc-ex-m reduced the
maximum glass surface temperature by 17.05% compared to the baseline case, and
20.26% compared the baseline case with shading (Figure 132). Moreover, the thermal
comfort level for occupants in the north facing room has increased from 90% for both
baseline cases to 100%.
182

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal perofrmance of scenario 058-b-n-150-rc-ex-m

Figure 132 Thermal performance for scenario 058-b-n-150-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)
In this case, thermal performance has improved due to several elements; extra shading
that the box-window cavity’s dividers provided in addition to the glazing properties
helped to reduce the amount of received solar gain on the northern rooms. Furthermore,
injecting exhaust air inside the cavity helped to reduce the air temperature inside the
cavity and surface temperatures.

183

6.4. Ventilation and airflow performance
This section evaluates and analyzes the cavity’s ventilation influence on energy
consumption and thermal performance. Most of the scenarios’ results have minor
differences; however, the most effective scenarios with highest values have been chosen
to be analyzed. For each scenario, we are going to look at: results review, a comparison
to the baseline cases, and an analysis for the behavior of the scenario.
6.4.1. Natural Ventilation
6.4.1.1. Energy performance:
Total energy consumption for double skin facades naturally ventilated cavity scenarios
are ranging between 376.3 – 359.9 MWh (217.8 – 208.3 kW/m
2
). 075-b-w-150-rc-ex-n
showed the most improved performance in terms of energy consumption. This scenario,
which faces west and has 150cm cavity with naturally ventilated cavity, has total annual
energy consumption of 359.9 MWh (EUI = 208.3 kWh/m
2
). Cooling energy/m
2
value is
(80.7 kW/m
2
). For the western room which adjacent to the cavity, total space
conditioning sensible in the peak day (6
th
of August) is (-93.48 kW), and maximum solar
gain is (1.78 kW).
In comparison to west facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 6.56% compared the baseline case, and a reduction of
3.25% compared to the baseline case with shading. In rooms facing west, space
conditioning sensible in the peak day was reduced 25.44 % compared to the baseline
case, and reduced 18.44 % compared to the baseline case with shading (Figure 133).
184

Maximum solar gain in the peak day also reduced 77.61% compared the baseline case
and reduced 50.52% compared to the baseline case with shading (Figure 134).
24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
Peak day hours
Space conditioning sensible (kW)
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
075-b-w-150-rc-ex-n
V ariable
Space conditioning sensible (kW) for 075-b-w-150-rc-ex-n

Figure 133 Space conditioning sensible (kW) for scenario 075-b-w-150-rc-ex-n and baseline cases in
peak day (6th of August)

185

24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (150cm cav ity )
V ariable
Solar gain in peak day for scenario 075-b-w-150-rc-ex-n

Figure 134 Solar gain (kW) for scenario 075-b-w-150-rc-ex-m and baseline cases in the peak day (6th
of August)

Figure 135 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 075-b-w-150-rc-ex-m (right)
186

075-b-w-150-rc-ex-n showed the best energy performance among west facing scenarios
with different configurations. Extra shading provided by box-window type’ s cavity and
glazing type have a significant impact in reducing solar gain and minimizing the cavity
volume to avoid overheating. The combinations of the mentioned elements provided
reduction in energy consumption compared to baseline cases. Injecting natural ventilation
inside the cavity helped to extract the heat in the cavity and reduced the surfaces
temperature for the inner skin, which also, helped to reduce the cooling loads and
improve the energy performance.
6.4.1.2. Thermal performance:
Inner glass maximum surface temperature for scenarios with 150cm in the peak day are
ranging between 31.34
o
C – 29.56
o
C . Scenario 057-b-n-150-rc-ex-n, which faces north
and has 150cm cavity depth with naturally ventilated cavity, has an improved thermal
performance among scenarios with naturally ventilated cavity and baseline cases. In the
peak day (6
th
of August) the maximum air temperature inside the cavity is (45.90
o
C) and
the average is (38.08
o
C). Maximum surfaces temperature for the glass (Inner skin) is
(29.56
o
C) and for the wall is (25.23
o
C). All the scenarios with naturally ventilated cavity
have thermal comfort level of 100% during the occupational hours.
In comparison to the north facing baseline cases, 057-b-n-150-rc-ex-n reduced the
maximum glass surface temperature by 13.54% compared to the baseline case, and
16.9% compared the baseline case with shading (Figure 136). Moreover, the thermal
comfort level for occupants in the north facing room has increased from 90% for both
baseline cases to 100%.
187

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal perofrmance of scenario 057-b-n-150-rc-ex-n

Figure 136 Thermal performance for scenario 057-b-n-150-rc-ex-n, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)
In this case, thermal performance has improved due to several elements; extra shading
that the box-window cavity’s dividers provided, external shading, glazing type and
injecting natural air inside the cavity helped to improve inner surfaces temperature
providing more comfort levels compared to the baseline cases.

188

6.4.2. Integrating HVAC system to the facade
6.4.2.1. Energy performance:
Total energy consumption for double skin facades mechanically ventilated cavity
scenarios are ranging between 371.5 – 354.2 MWh (215 – 205 kW/m
2
). 076-b-w-150-rc-
ex-m showed the most improved performance in terms of energy consumption. This
scenario, which faces west and has 150cm cavity with mechanically ventilated cavity, has
total annual energy consumption of 354.2 MWh (EUI = 205 kWh/m
2
). Cooling
energy/m
2
value is (78.6 kW/m
2
). For the western room which adjacent to the cavity,
total space conditioning sensible in the peak day (6
th
of August) is (-82.34 kW), and
maximum solar gain is (1.78 kW).
In comparison to west facing baseline cases, the mentioned scenario showed a total
energy consumption reduction of 8.04% compared the baseline case, and a reduction of
4.78% compared to the baseline case with shading. In rooms facing west, space
conditioning sensible in the peak day was reduced 34.32% compared to the baseline case,
and reduced 28.16% compared to the baseline case with shading (Figure 137). Maximum
solar gain in the peak day also reduced 77.58% compared the baseline case and reduced
50.41% compared to the baseline case with shading (Figure 138).
189

24 22 20 18 16 14 12 10 8 6 4 2
0
-2
-4
-6
-8
-10
-12
-14
Peak day hours
Space conditioning sensible (kW)
001.4-s-w-na-rc-na-na baseline
005-s-w-na-rc-ex-na
076-b-w-150-rc-ex-m
V ariable
Space conditioning sensible (kW) for 076-b-w-150-rc-ex-m

Figure 137 Space conditioning sensible (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in
peak day (6th of August)
190

24 22 20 18 16 14 12 10 8 6 4 2
8
7
6
5
4
3
2
1
0
Peak day hours
Solar gain (kW)
Baseline
Baseline with shading
Box-window ty pe (150cm cav ity )
V ariable
Solar gain in peak day for scenario 076-b-w-150-rc-ex-m

Figure 138 Solar gain (kW) for scenario 076-b-w-150-rc-ex-m and baseline cases in the peak day (6th
of August)

Figure 139 Solar gain and space conditioning sensible (in the peak day) comparison between baseline
case (left), baseline case with shading (center), and scenario 076-b-w-150-rc-ex-m (right)

191

076-b-w-150-rc-ex-m showed the best energy performance among west facing scenarios
with different configurations. Extra shading provided by box-window type’ cavity has a
significant impact in reducing solar gain and minimizing the cavity volume to avoid
overheating. The combinations of the mentioned elements provided reduction in energy
consumption compared to baseline cases. Injecting exhaust air inside the cavity reduced
air temperature inside the cavity and surfaces temperature for the inner skin, which also,
helped to reduce the cooling loads and improve the energy performance.
6.4.2.2. Thermal performance:
Inner glass maximum surface temperature for scenarios with mechanically ventilated
cavity in peak day are ranging between 31.46
o
C – 28.36
o
C . Scenario 058-b-n-150-rc-
ex-m, which faces north and has 150cm cavity depth with mechanically ventilated cavity,
has an improved thermal performance among north facing scenarios and baseline cases.
In the peak day (6
th
of August) the maximum air temperature inside the cavity is (37.15
o
C) and the average is (29.57
o
C). Maximum Surfaces temperature for the glass (Inner
skin) is (28.36
o
C) and for the wall is (24.56
o
C). All the north facing scenarios have
thermal comfort level of 100% during the occupational hours.
In comparison to the north facing baseline cases, 058-b-n-150-rc-ex-m reduced the
maximum glass surface temperature by 17.05% compared to the baseline case, and
20.26% compared the baseline case with shading (Figure 140). Moreover, the thermal
comfort level for occupants in the north facing room has increased from 90% for both
baseline cases to 100%.
192

24 22 20 18 16 14 12 10 8 6 4 2
45
40
35
30
25
Peak day hours
Temperature (°C)
Dry-bulb temperature (°C)
Ait temperature in the cavity
Inner glass temperature
Baseline glass temperature
Baseline with shading glass
Variable
Thermal perofrmance of scenario 058-b-n-150-rc-ex-m

Figure 140 Thermal performance for scenario 058-b-n-150-rc-ex-m, measuring inner skin (glass)
surface temperature in comparison to baseline cases in peak day (6th of August)
In this case, thermal performance has improved due to several elements; extra shading
that the box-window cavity’s dividers provided and glazing type in addition to injecting
exhaust air inside the cavity helped to reduce the air temperature inside the cavity and
surfaces temperature, providing more comfort levels compared with baseline cases.

193

7. Chapter Seven: Conclusions $ Future Work
7.1. Summary:
Buildings in hot-arid climate areas are major contributors of the vast energy consumption
due to their enormous demand of mechanical air conditioning. In Riyadh city, office
buildings currently are designed with high glazing areas because of their aesthetic value
without considering the climate conditions and without applying proper strategies to
provide protection from the harsh environment. Recently, many reports from government
agencies in Saudi Arabia have stated that the buildings are consuming the largest
percentage of the national electricity production. Looking for innovative strategies to
meet and balance both the clients' and environment requirements was the motive to do
this research project. It’s believed that double skin façades with proper configurations are
able to help to improve the energy consumption and increase comfort levels by
improving the thermal performance of facades. After looking in several previous studies
and built examples in the same climate, we came up with a better understanding about
how to optimize the configurations of double skin facades in hot-arid climates. A list of
proposed variables has been conducted to be examined in several double skin façade
scenarios. For scenarios, this research adopted a thermal dynamic simulation program,
IES-VE, on a hypothetical office building in Riyadh city. Several ineffective variables
were removed to reduce the amount of cases tested without jeopardizing the results. The
energy and thermal performance for each scenario were calculated, and compared to
baseline cases which have no double skin façade applied to the building envelope. As a
final step, the best performed scenario and most effective configuration of each building
194

façade has been reviewed and analyzed to assess the influence of each selected façade
components on the building energy and thermal performance.
7.2. Conclusions:
The study confirms the hypothesis within the scope and constraints tested. Most of
double skin façade scenarios showed significant reduction in energy consumption
compared to baseline cases for the same building. Results vary between different
scenarios based on their examined variables. However, the most effective configurations
occur when the cavity was located on the western and eastern facades and used wider
cavity depth with a mechanically ventilation. This combination provided extra protection
compared to single skin facades and reduced of the amount of solar gain in the rooms
adjacent to the cavity, thus cooling loads were decreased. In addition, the inner surface
temperatures were dropped due to the injected exhaust air from the HVAC system.
Using different double skin façade typologies such as multi-story, corridor type and box-
window generated differences in reduction of the energy consumption compared to
baseline cases. For instance, locating the cavity in the western façade, which was the
most effective location of the double skin façade, reduced the energy consumption for
multi-story type by 5.02% compared to the baseline case, and 4.05% compared to the
baseline with shading. The corridor type façade reduced the energy consumption over the
baseline by 7.71% and 4.43% compared to the baseline with shading. In the case of the
box-window type, 8.05% and 4.78% of the energy savings were estimated compared to
the baseline without and with shading, respectively
195

All the tested double skin façade scenarios showed that the predicted percentage of
dissatisfied occupants (PPD%) are always ranging between 5-15% which means the
majority of the occupants find the rooms adjacent to the cavity during the occupation
hours in the peak day (6
th
of August) in the comfort levels, unlike the baseline cases
where thermal dissatisfaction rate was significantly higher than 15%.

7.3. Research limitations:
This study adopted a simplified HVAC system was used in the building, which may
affect the accuracy of the results and may show less efficient results than other systems.
However, it was intended to choose this to make all of the results comparable and able to
be analyzed. A VAV with economizer HVAC system was used at the beginning,
however, it needs deep experience and complexity to model it with the mechanically
ventilated cavity scenarios especially with corridor and box window types because they
use several air outlets, which make it problematic to model them.
Reflective coating glazing was chosen instead of the Low-E glazing on the external skin
because of its improved results in terms of energy and thermal performance; however,
reflective coating glazing can limit the amount of transmitted daylight in spaces adjacent
to the cavities.
Furthermore, shading devices on the external skin were chosen instead of the inside of
the cavity because of the improved results in reducing the energy consumption and
mitigating the air temperature inside the cavity and interior surface temperatures;
196

however, exposing the louvers without protecting them against the environmental
conditions would have negative effects on the durability of the shading devices. Also, the
accessibility to louvers for the maintenance would be an issue that can prevent the
proposed configurations from being practical practices.

7.4. Future work:
Most results were obtained from computer simulations of a hypothetical building. On-site
measurement for existing buildings, or tests on a mockup model are needed to validate
the acquired data.
Some of the adopted variables such as, the glazing type and location of the shading were
selected based on their energy and thermal behavior; though, they might limit and have
undesired effects on other factors including day-lighting, durability of materials and
maintenance issues. Further investigations considering the mentioned factors are required
to find out the optimum double skin façade configurations.
This study examined the effect of double skin façade influence on improving energy and
thermal performance in Riyadh’s climate. Ventilatin g the cavity, whether using natural or
mechanical ventilation was one of the testing variables to reach the goals of this study;
however, using hybrid systems may expand the possibilities that double skin façade can
provide in terms of energy and thermal performance.
This study adopted a simplified variable air volume (VAV) system, which might show
less efficient results than other systems. Further studies are required to simulate advanced
197

mechanical settings, especially with corridor and box window types due to their
sensitivity to air outlets from the mechanical systems.
Finally, one of the main characteristics of Riyadh’s climate is continuous dust storms
during the summer. A study of filtering the natural air from dust particles should be
carried out to examine the possibility of providing natural air in this climate.
The study confirms the hypothesis within the scope and constraints tested

198

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Abstract (if available)

Abstract Due to the vast development in construction in hot-arid climate areas, implementing innovative façade technologies is crucial to meet owners and developer needs, and to meet climate conditions requirements. Buildings are major contributors of energy consumption due to the high glazing areas and their role of increasing cooling demand. Double skin facades are used in cold and temperate climates to reduce heating loads and for other benefits

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Asset Metadata

Creator Alahmed, Zakarya A. (author)

Core Title Double skin façade in hot arid climates: computer simulations to find optimized energy and thermal performance of double skin façades

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Publication Date 08/05/2013

Defense Date 05/13/2013

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag double skin facade,energy saving,energy simulation,hot arid climates,OAI-PMH Harvest,Office Building

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Noble, Douglas (committee chair), Choi, Joon-Ho (committee member), Schiler, Marc (committee member), Vaglio, Jeffrey (committee member)

Creator Email alahmedzak@gmail.com,zakr@hotmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-316327

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Dmrecord 316327

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Rights Alahmed, Zakarya A.

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Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

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